They can't expel people for things they do off campus. That is true. However it also shouldn't be the case, as we had our wave of "red scare" persecutions of people in the 70s, destroying peoples lives based on often farbicated charges against people who were considered "too left".

Denying people access to education based on criminal charges is a slippery slope and in the current environment it is likely, that these will solely be used for political persecution.

Also it should be noted that the claim, that the attack was bigotry related is made by the victim and his supporters, with the victim having a history of violently engaging pro palestinian protestors on campus, ripping off posters that remembered killed palestinian women and children and repeatedly demanded all pro palestinian voices to be banned from campus.

The police didnt classify it as a hate crime so far and the claims of it being a hate crime are made on the allegation that jewishness and pro-israel and pro-zionism stances are identical. (Which is in itself antisemtic and used to repress jewish people in Germany who are critical of zionism)