If I recall correctly, it was worse than that. Stephie asked him if he knew about Flynn, and in his answer he said he didn't know anything about the "investigation" of Flynn. Stephie, knowing Biden just stepped in clinton, reminded him that he was in the January 5, 2017 meeting with the rest of the conspirators. Biden then said , oh, I thought you said "prosecution", yes I knew about the investigation, but that's it. He knew nothing else. He lied with his own words by previously saying he didn't know anything about the Flynn investigation.
Pretending to be an addle-brained old fart is going to come in handy for him for a while, if “CRS” is a valid excuse.