I don’t know if any/many Jews/Israelis actually celebrated, and if they did then why would that be; but the conspiratorial accusation towards Jews/Israelis in particular is that they caused or at least celebrated the attack because it would drag the US into fighting Israel’s enemies in the ME.
Separately, I could imagine [anyone who’s generally been a continual target of Islamic extremism] not exactly celebrating but (unwisely) seeing the upside “well at least now you get it”.
(I will abstractly state that I feel negatively towards the group dynamics around some AI debates in the broader EA/LW/AI/X-derisking sphere, e.g. about timelines; so, affirming that I feel “knee-deep” in something, or I would if my primary activity were about that; and affirming that addressing this in a gradual-unraveling way could be helpful.)