What “meaning” did he need to clarify? Denying he called her nasty was correct. Only the liberal media (and perhaps you) didn’t understand what he said originally.
“I didn’t know she was nasty” could easily be taken as “calling her nasty” by the average person.
Would have been better to clarify his intended meaning as though it was all a no big deal which it wasn’t.
Much less downside then trying to deny saying something that a fair % of right minded people could interpret either way.