The Powder Toy came out about 3 years after The Powder Game and there was "The Falling Sand Game" considered to have kicked off the genre to popularity (video: https://external-preview.redd.it/KbiveNFl8yr3yJ0znWqoZM-7sIa...) which came out about 2 years prior to either (~2005).

Of course nothing is ever fully original and you can continue to trace back to an older "classic" if you like.

Powder game is the first I was aware to have a pressure system. There were of course falling sand games before that.