[your work product belongs to the employer]
Let's get this straight.  Simply because the conversation happened between Comey and Trump it became "work product?"  I don't know where you work but that would be called slavery in here in the United States.  In fact, there are a lot of labor law cases where personally kept productivity diaries, often in regards to contractually required raises, are patently not work product, protected trade secrets, etc.
[he wrote an official note]
Source?  Just about every article I can recall reading indicates Comey's notes were not official but personal.  They were prompted by his personal feelings and impressions of distrust for Trump.  Information recorded in written or digital format does not automatically become work product simply because it involved a discussion with a coworker, employer, etc.  Last I checked, Comey's job didn't require or involve anything even loosely translatable to call his personal recordings "work product."