He said he got a (self arranged and paid for) flight the same night on El Al.

OP would need to confirm the difference between the original BA scheduled arrival and his actual arrival time on ElAl to see if EU261 applies.

akso it’s possible (and I’m not an expert) that as Israel is involved their equivalent of EU261 may kick in and that could be better option for the OP to claim against but he would need to investigate that further.

the urgent need is to ensure his return has been protected and his luggage