The homophobia doesn't account for him getting his ass kicked, it certainly does for the zero.
complete bullshit.
there were like 7 or 8 candidates that got zeros with sc black voters and another handful with 1s and 2s, almost all of whom have more experience in government, more impressive resumes and have demonstrated more interest in speaking with black voters than buttigieg. you don't have to look for anything extraneous beyond the fact that the voters preferred other candidates to explain those numbers. buttigieg is a mayor of a small town with no relevant experience, a miserable record of governance in his own town and no history of engaging black voters much less black voters in south carolina. he's polling at about 8% nationally, up in the last couple of weeks from about 5% where he was at since june or so. the anomaly isn't that he's polling at 0% with black voters in sc, it's that he's suddenly polling at 20+% in iowa.
your notion also makes no sense statistically. homophobia is slightly more prevalent among black americans than white americans (almost entirely a function of black americans being more religious) and significantly more prevalent among black democrats than white democrats (a function of white americans with more homophobic attitudes being more likely to be republicans than is the case among black americans), but that doesn't mean that every last black voter in south carolina is homophobic. i haven't seen data on black voters in sc specifically, but i just saw a survey that said 31% of natl democrats said, all things being equal, they'd be less likely to vote for a homosexual candidate (not wouldn't vote for, just less likely). even if you double that for sc black voters, a number which assuredly is too high, that's 60% that might be some degree more reluctant to vote for buttigieg than other candidates due to negative attitudes re. homosexuals. buttigieg got 0% of the other 40% too.
like, if i had access to that dataset and did a statistical test to determine if attitudes towards homosexuals explained any variation between the likelihood of voting for buttigieg among black voters in sc, the result would be that it doesn't, because there is no variation among black south carolina voters in likelihood of voting for buttigieg.