He played in 3 games and quit (this, after it didn't go well at his previous school). Without giving it much thought, I'd probably drop him from the roster too. Not out of any sort of spite or resentment and not sure why you would suggest it is a retaliatory petty move. Why have someone who isn't part of the team show up as part of the team? I would prefer my roster to be an accurate reflection. Simple as that.
But as others have said, could be tons of different reasons. I also agree with several others... why would it matter? It's not like there are significant stats, good or bad, meaningful to the team or player. Probably doing the kid a favor, if anything. Should he pursue another school, dropping out and quitting may or may not have been for valid reasons but is hardly a good look, particularly if this is the second time things didn't go well. Heck, the removal may have been at the kid's request. We could speculate all day.