they canceled the linux version for postal 4, so i am pretty sure they mean proton

iirc Postal 4 native linux isn't cancelled, it's just low-priority; and even if it was cancelled, that's mostly because Unreal Engine is horrible at making Linux ports and they'd be spending a bunch of time making a port that may not even run well. This is using Unity which, while not perfect at native ports, is a far cry from the nightmare Unreal Engine is and so I can see them springing for a native port. RWS definitely has vested interest in Linux given how long they've supported the platform, even well before it was as prominent as it's becoming now. I could see them wanting to get back into native Linux support given how long it's been since their last game to natively support Linux, the original Postal Redux.