Looks like he's counting plies rather than moves, and the spike at the 80th ply is caused by the 40-move time control

http://www.fide.com/fide/handbook.html?id=39&view=category

I'm interested to know whether the "draw if 3 repeated moves" was applied. (Technically in the rules the draw is offered to the other player I believe? But it is almost always taken if it got to that point.)

If not this could lead to some very long games observed.