I just listened to it over and over.
I do NOT believe he said “not”.
I heard, with a frog in his throat or a mis-forming of the words, “I’m a Christian”.
Listen again with THIS in mind NOT the salacious attempt to make it seem he said “I’m not a Christian”
“I’m a Christian”.
“I’m a Christian”.
“I’m a Christian”.
“I’m a Christian”.
I’ve now listened several times and I’m still get the ‘I’m not’. I still figure he simply misspoke as he frequently talks about religion and his faith.