It is antisemitic in universe, and it's obviously a parody of antisemitic behavior. Comedy and parody typically get a pass on offensive behavior, particularly when the offender is being mocked and the language is being used as criticism (see racist and antisemitic content in Mel Brooks films, for example.) Some people probably do find Borat offensive, and Mel Brooks, regardless.

But I think the mistake your comment makes is trying to find an objective definition to judge a subjective behavior, trying to determine whether people should find something antisemitic, regardless of the context. But sometimes context does matter and you can't really control who gets offended at what, or judge what offense is "legitimate" and what isn't, based on some arbitrary criteria.