I thought the same Gam, but the 'ring is different rules to your regular track day. You are supposed to overtake on one side (I think) but from all the 'ring videos I've seen it looks like a bit of a free for all.
At a guess I'd say the guy is/was a race driver (be it karting, cars etc) or just a VERY committed track driver as he seems to have no fear of swapping paint with someone. That kind of attitude tends to come from someone whos been there and done that.
UK track days tend to be much more disciplined and overtaking on the correct side, indicating and not diving up somones inside mid corner like some crazed lunatic tend to be rules people (for the most part) stick to