> Unless I missed that the hearing was highly related to this, why would he remember this exact date offhand?

Because it is one of the biggest scandals affecting Facebook in probably its entire history, and he's been grilled about it before? You'd think that once they found out his staff and advisors would make sure to tell him every single detail about it. Likewise, it should be the thing that occupies him for months on end.

It's inexcusable for him to not seem to know some basic factoids about the whole thing.