This would be my guess. It's hard to imagine Kasparov didn't notice. There are variants of chess where the pieces are organized differently and obviously as the game progresses beyond the opening you can get into all sorts of positions. I'm sure Kasparov can calculate from any given arrangement of the pieces. The difference would be that moves that he would play automatically because of preparation now have to be thought through deeper.

I'm impressed parent survived that many moves. Must be a good chess player even with the simultaneous game setting.

That's what I think, and also what I think I wrote. Sorry if it's unclear, I'm not a native English speaker.