What was this guy doing on his tablet - game, or music, or dexterity exercise?

In My Humble Opinion
1

I was sitting opposite this young, probably Asian man (if that makes a difference) on the BART train who had a tablet on his lap, with earphones plugged in. It was what I would call a full-sized tablet. On the tablet the software showed a grid of fairly large squares, maybe 4 across and 6 down (I didn’t actually count them). When any square showed purple (as far as I could see) he touched the square with a finger as fast as he could. Sometimes he would touch with individual fingers in rapid sequence, sometimes he would touch several squares with several fingers at roughly the same time. The pattern of purple squares seemed random but it also seemed possible that it might have been linked to something he was hearing in the headphones. The headphones were of the style that I think of as noise-cancelling. He was very fast and I couldn’t really follow it fully from where I was sitting.

Anyone have any idea what he was doing? I tried googling this but couldn’t find anything.

2

Sounds like some sort of music sequencer app or similar - here’s one

They are apps that simulate this sort of physical appliance: https://www.youtube.com/watch?v=gMgxLPcq-3o
3

Hmm, it was closer to the second one, although with many fewer squares, and his hands were moving really fast. Thanks. Although I don’t really understand what the purpose is.

4

Piano Tiles?

5

Could have been all three.