Oh no! But I really don't think you have to gaslight the dude. Just say you meant to mention it but didn't manage to fit it into the conversation, and then too much time passed and it was too awkward to mention. I feel like that's better than pretending you told him.

Like, we've all had that thing we didn't mention and now it's awkward that we didn't mention it. I feel like it's not a big deal, esp with coworkers where you're not close socially.