Well Trump does have a good reason for believing private conversations with the FBI director over sensitive subjects are okay.
Did you listen to the Comey testimony?
Comey detailed out how in their very first meeting with Trump as President elect he at the end of the meeting told everyone else to leave the room so he could have a private meeting with Trump. They discussed the now debunked “dossier” that was being spread all over the place and it was then that Comey first told Trump that he was not under any kind of investigation.
At that time Comey established that style of meeting was indeed normal, how was Trump to know it was not when a lifetime bureaucrat like Comey was making it clear it was okay?