So this guy heard that Israel had been warned of the attacks ahead, and he thought they had failed to act on this because they wanted to have an excuse to attack Hamas?
It's not just speculation, but pretty accepted, that Hamas is quite happy to draw attacks on the Palestinian people so as to create sympathy for them, and turn people against Israel.
States do things like this too, and it would not shock me to find Israel had done something similar. The question is whether it is true. But I'd not dismiss it out of hand.
If Ali really believed this is what happened, I don't think it would have to suggest any kind of antisemitism. If he repeated it despite knowing it wasn't true, that might suggest antisemitism.