From reading the NYTimes article [1] it seems clear he’s anti Israel/occupation/bombing and not anti semitic. The pro Israel groups that sought to oppose him getting the job didn’t try to argue that he was anti semitic either, just that he wasn’t ‘civil’ on his Twitter feed.
1) you can criticize Israel all day on campus, no one will stop you.
2) you shouldn’t promote mass murder on campus, which is what SS did. Saying the population deserves mass murder because they’re evil is what he did. Fortunately that was deemed beyond the pale.
A brief read of the tweets included in the article he links to regarding his firing gives me the impression that it's the latter. In fact there is one tweet of his which references exactly your point about the deliberate confusion of anti-Semitism and legitimate criticism of Israeli policy.
Shame that he continues to be anti-Semitic in his tweets.