Lots of people actually misremember, or outright lie, about these matters. For example, with 9/11: https://www.scientificamerican.com/article/911-memory-accura...
So him actually not remembering isn't that surprising.
I was in my car commuting to work, and very annoyed at what sounded like some kind of tasteless radio prank. I turned it off and only upon arriving at the office realized it was actually happening.
That's how my "where were you when you heard about 9/11" goes. I confidently had an answer for decades, but a few years ago discussed it with my father who I remembered telling me, and he doesn't remember it the same way. So now I'm not sure whether either of us remember it correctly.
Regardless of the accuracy or implication of where he was or wasn't, which I have no comment on or knowledge of, you are claiming that a government official not remembering he was merely a block away from where the president of the United States was assassinated not that surprising? I could imagine details, like the hotel or street name, being misremembered, but what you're claiming is hard to believe.
I was in Toronto just 20 days before 9/11. Was I a co-conspirator? No.