There's no way that's how the First Amendment works with Social Media. Just because a listener could read your words in a particular spot doesn't give the government free reign to impose time place and manner restrictions based on where the words were read.
huh? Did I say that?
I'm not even saying this guy's initial post was disruptive, I just disagree with your assertion that the time and location of a social media post really matters if it contains threatening or disruptive content. (Maybe there is legal precedence, when I read the summary linked in the original article it seemed like it's still being figured out)
I guess I could have misread what you meant, but I think you did say that with this:
Eh I think it's pretty different with social media - "where the speech occurred" is really "everywhere" when you post crap online. Fellow students saw it, so it was like yelling "eff ABORTIONS" within clear earshot of everyone in his school. Which, even if it wasn't directed at anyone in particular, could arguably be disruptive to class.
My point is that, there is an absolute clear and rational difference between speaking in a classroom during a class and posting something to FB, twitter, or gE. Time/place/manner restrictions have been recognized forever and they make perfect sense.
I agree that if the online opinion was threatening (within the meaning of the first amendment), then the time and place at which he made it isn't significant. I don't think it's correct to stretch "disruptive" to that same extent. Otherwise, any online opinion some students disagree with could be labeled disruptive. If you don't like someone's spicy hot political takes online (or on TV, or in a book or painting or song), you have a range of options: don't friend them, don't follow them, ignore them, read them for fun, think worse of the person, do whatever you want. We're all subject to opinions we disagree with every day.
If someone disrupts class though, you can't help but be subject to that disruption. If gone unpunished, that student has free reign to continue to waste the time and money of those teaching and attending the class. I don't think a school or any other government body has any right to punish a student for tweeting that "BLACK LIVES MATTER" (despite its potential to offend), whereas I think an outburst like that (or "ABORTION IS MURDER") is certainly punishable if shouted out during the middle of a Chem 200 class.
Generally speaking, the government entity shouldn't have any more authority over your online speech than it does over your speech in any other public forum -- which is to say, it should have next to none.