While both are infringement on intellectual property, the cardinal difference is that plagiarism is stealing someone else intellectual work and passing it off as your own product. With piracy the pirate doesn’t claim they themselves made the game, nor do they resell the game for profit.
In my hometown there was a spot near the main square that was just far away enough that to go there you really had to go out of your way.
For years there used to be a pozzeria there and after they closed it down, a kebab decided to open there. It only lasted about two months before the owner gave up because literally no one would go there when there were already three other kebabs on the square, and in far more convenient places.
That didn’t deter a bunch of other geniuses from opening their shop there, because throughout the next two years five different kebsbs opened there, before finally the barber nextdoor bought it out and integrated that space into his barbershop.