As I mentioned before, stating you "you don't remember anything" at the point of questioning by anyone is a smart legal play IMO.
Yesterday, what did I do?
Went to the office for work, came home, sent off some emails, picked up my mower for service, worked the compost pile, collected leaves for the compost pile. Now, ask me what was exactly said during my office trip, at the mower shop (owner who I know very well) and what my wife and I specifically talked about, I honestly don't remember and have to think about it.
Irvin IMO honest opinion was honest with his answer. Thing is, we're assuming he doesn't remember anything, but is that not remembering the entire night? Or who you were with and exactly what was said?
If he was really "hammered", I'm certain more people would be coming out saying he was drunk, slurring his speech and couldn't walk straight.
Had my boss ask me last week about an incident last year. Told him I honestly didn't remember the exact circumstances. Took me a couple of days and thinking about it, it hit me on what was actually said and done, and the same thing for my co worker (he didn't remember what I thought I did, but after a day, he told me he remembered it, and it was pretty much my story). Peoples memory and exactly what they remember and when can be a tricky science. This is one of many reasons why eyewitness accounts taken "on the spot" of an event can be misleading. Lots of people were hung because of what one person said what they saw, believing the eyewitness.
Only hard evidence is the video, and unless you can hear the conversation, I'm learning towards nothing happened.