(Emphasis, mine). I suspect that he understood functional languages quite well.
He just didn't like them.
I like some aspects of FP, but there are other aspects that I don't like.
My own development style is a ghastly chimera of techniques, technologies and jargon that coagulate into a disgusting bouillabaisse that makes everyone go "tsk, tsk," but that always seems to work quite well, is of extremely high quality, easy to understand, and results in a great deal of ship.
I am...impure. All zealots hate me.