His beef against physicists is likely rooted in confirmation bias. Musk has a BA in physics that some debate if he even completed, but one bad egg does not prove the rule. It would be just as easy to point out engineers who have gone on to lead dodgy enterprises but, again, a few bad eggs do not prove the rule.

His reason for attacking another group is likely to make his own group look superior. This works on the playground and in more professional situations than it really should. He might also just be airing his prejudices thoughtlessly.

Either way, it's probably going to limit the audience he reaches and invite some nasty responses. He'd do well to avoid spewing such nonsense in the future.