It’s the FBI Director writing a memo on topics for which he should be completely familiar with classification guidelines. No reasonable person could conclude that he made an innocent error on the classification of his private discussions with President Trump on this topic. If the memo contained classified information, that could not be an accident or due to a lack of knowledge of what is classified.
I spent most of the past year assuming that Comey was a moron who made multiple serious but unintentional errors in judgement. Occam’s Razor led to the conclusion that Comey was over his head and made bad decisions on the Hillary investigations. Given the ongoing pattern, I apologize for thinking Comey was an intellectual clown. He’s not a fool - he just thinks he can fool all of the people some of the time.
While FOUO is not a classification, it does provide handling instructions.
Any private meeting with the President based on your official position (e.g., not as a fundraiser) would be at least FOUO, but more likely have classification implications.