Only direct damage contributes to rage fist counter.
https://www.smogon.com/forums/threads/scarlet-violet-battle-mechanics-research.3709545/page-13 (post#312)
Then it's implemented very incorrectly on showdown
After discussing, it turns out that our amazing development and coding team already was made aware of this prior and is implementing a fix in the immediate future.I am inquiring internally on this matter
Direct, turn-of damaging attacks impact Rage Fist. Any other move does not. Think of it like moves that would trigger Counter or Mirror Coat (in the wise words of Lily). This means things like Poison damage no longer impact it.
I also want to thank Marty for his timely and helpful response to all of my inquiries thus far. All of the PS contributors have been professional, timely, and very explanatory so far.