I'm going to guess here but I'm thinking that's a mixture motion piston top (my limited education stops me from giving a better description) to induce a more homogeneous mixture. Or maybe it helps suppress detonation in some way. At 60 pounds of boost for that time frame I'm sure that detonation is an enemy.

The thing that stuck out more than that to me, was the fact he was using a gapless top ring. Some would say the engine builder is stupid for that, because they don't work.

Just weird things you see sometimes.