3 F'ing things. First, there's an old saying in the Army...

[Nasruddin]

41. He got it

Perhaps Kelly was trying to coach Trump's responses, and Trump garbled it.

Usually, successful sociopaths or psychopaths have this down long before they're 70!
It's not such a difficult thing and they are usually pretty good at sizing other
people up and learning what the useful things to say and do are.
They don't come by their reputation for charisma purely genetically.
Maybe this really was such a strange new situation for DJT that he didn't
have a human race script ready.

Perhaps DJT is too limited at this point in his life, or he was too angry at
feeling forced to make this call, and he made a hash of whatever Kelly
was trying to do with him.

The gift to us is we learned who and what Kelly is.