Gawd. Sessions volunteered a false answer that didn't answer the question directly.
https://www.realclearpolitics.com/v...ons_about_russia_in_confirmation_hearing.html
He could have just said "Well, I'd have to look into it." Easy-peasy & skate right on by. But that's not what happened. If his meeting with Kislyak ever became public knowledge he could say nobody asked him about it & be telling the truth.
As you've said, it can be easy to forget. OTOH, I seriously doubt that Sessions forgot about meeting with Kislyak in his own office a few months earlier. It's not something he'd do everyday.