Virtually every commentator on the Comey firing has puzzled over the inclusion by Trump in the termination letter of a sentence in which the President mentioned three occasions on which Comey had said the President was not under investigation. I'm not certain why it's puzzles.
It seems clear to me Trump was establishing he had no conflict of interest in the firing. He was not interfering in an investigation of himself, inasmuch as he understood no such investigation was underway. The only confusing part is why he thought Democrats or the media (I repeat myself) would pay attention thereto.