I think he just means that sexual harassment is different from "heat", however you want to define that.
Correct.
> In other words, to be complained about/insulted/whatever.
No, that's not what that means. To catch heat or flak is angering / upsetting others due to your actions then being on the receiving of said anger. It has nothing to do with one sided insults.
I don't really know how much evidence is in any of those claims (I thought there was supposedly evidence, not zero, but I really don't care enough to bother looking anyway) as I never really wanted to talk or even fight about anything relating to Pao but I could see that changing the context for catching heat / flak if there is or isn't evidence.