You can't just take EEOC guidance and apply it to private citizens outside of the employment context. Pertaining to private conduct, harassment means something akin to criminal harassment in order to not be protected speech. And if you surveyed First Amendment case law in the U.S., you would see that you can't harass anyone without directing your harassment at a specific individual. Merely "harassing" a group of people (Blacks, Jews, etc.) in an abstract sense is not harassment. Look up Brandenberg v. Ohio, Virginia v. Black (Ginsburg's opinion on cross burning), and Nat'l Socialist Party of Am. v. Village of Skokie. So-called "liberal" and "conservative" justices alike tend to be on the same page when it comes to freedom of expression.
On the other hand, despite language such as "students do not surrender their constitutional rights at the schoolhouse gate," it is a fact that the Supreme Court has endorsed limiting the constitutional rights of students when classroom conduct causes a "substantial disruption" to classroom learning. However, those cases all deal with high school and below. To my knowledge, it has never been applied at the university level, where professors enjoy almost unlimited academic freedom. College campuses have long been considered the classic "public forum" where ideas can be exchanged without fear of sanction or censure. "Viewpoint discrimination," i.e. policies that target the content of speech, is particularly suspect. Some helpful background reading:
https://www.mtsu.edu/first-amendment/article/991/campus-speech-codesAny policy that could apply to this bonehead's tweet would almost certainly be unconstitutionally vague and overbroad, as the standard of review would be strict scrutiny, that is, the policy must be "narrowly tailored" to achieve a "compelling government interest." Narrow tailoring is a very high threshold, particularly in free speech law. The school will have to disclose who else it has punished under the policy (if anyone), and the student will point out thousands of rude, distasteful, disrespectful, harrassing etc. social media posts of other students and ask why the policy was not applied to them. The student will be able to make a pretty compelling case that he is being singled out and targeted merely for voicing an unpopular viewpoint (and one that wasn't directed towards anyone other than a dead man).
Some other perspectives:
John Stuart Mill, from On Liberty:
First, if any opinion is compelled to silence, that opinion may, for aught we can certainly know, be true. To deny this is to assume our own infallibility. Secondly, though the silenced opinion may be an error, it may, and very commonly does, contain a portion of truth; and since the general or prevailing opinion on any subject is rarely or never the whole truth, it is only by the collision of adverse opinions that the remainder of the truth has any chance of being supplied. Thirdly, even if the received opinion be not only true, but the whole truth; unless it is suffered to be, and actually is, vigorously and earnestly contested, it will, by most of those who receive it, be held in the manner of a prejudice, with little comprehension or feeling of its rational grounds
And Justices Brandeis and Holmes (Oliver Wendell) concurring in Whitney v. California:
Those who won our independence believed that the final end of the state was to make men free to develop their faculties, and that in its government the deliberative forces should prevail over the arbitrary. They valued liberty both as an end and as a means. They believed liberty to be the secret of happiness and courage to be the secret of liberty. They believed that freedom to think as you will and to speak as you think are means indispensable to the discovery and spread of political truth; that without free speech and assembly discussion would be futile; that with them, discussion affords ordinarily adequate protection against the dissemination of noxious doctrine; that the greatest menace to freedom is an inert people; that public discussion is a political duty; and that this should be a fundamental principle of the American government.
* * *
Believing in the power of reason as applied through public discussion, they eschewed silence coerced by law—the argument of force in its worst form. Recognizing the occasional tyrannies of governing majorities, they amended the Constitution so that free speech and assembly should be guaranteed.
Fear of serious injury cannot alone justify suppressions of free speech and assembly. Men feared witches and burnt women**. It is the function of speech to free men from the bondage of irrational fears.
* * *
Those who won our independence by revolution were not cowards. They did not fear political change. They did not exalt order at the cost of liberty. To courageous, self reliant men, with confidence in the power of free and fearless reasoning applied through the processes of popular government, no danger flowing from speech can be deemed clear and present, unless the incidence of the evil apprehended is so imminent that it may befall before there is opportunity for full discussion. If there be time to expose through discussion the falsehood and fallacies, to avert the evil by the processes of education, the remedy to be applied is more speech, not enforced silence. Only an emergency can justify repression. Such must be the rule if authority is to be reconciled with freedom. Such, in my opinion, is the command of the Constitution . . .
**highlighting this sentence because it has always stuck with me, and I've never read a 6 word sentence as powerful.