It's important to remember that Rebecca Long-Bailey didn't directly tweet the claim. She posted an interview that contained the claim, along with other things.
But I think anyone who thinks the claim wasn't anti-semitic should ask themselves two questions.
- Would it matter just as much if the US police had learned it from, say, MI5?
If the answer is "no" you are anti-semitic. It's just as unpleasant regardless of who they learned it from.
- What checking did the person do before making the claim?
If the answer is none or not much", once again we have anti-semitism. Ie, someone getting hot under the collar and repeating a claim that is lurid, because it's about Israel.
As for Rebecca Long-Bailey, there are only two possibilities, neither of which reflect at all well on her. Either she believed the claim, which would make her an anti-semite. Or she formed no view on it before publishing it, which shows lack of judgement by her concerning what information she repeats.
Perhaps the moral of this is that all people (but politicians especially) should be careful not to repeat crap on the Internet.