What is religion, if not conjecture about the origin of mankind (and by extension the universe) that people believe without evidence?
Religion identifies the simulator and insists that its intermediaries can offer a liaison between you and them, and also that if you don’t believe in their particular simulator, you will be punished. It has been used for centuries to control the populace and to take their money.
A proponent of simulation theory isn’t likely to tell you that it solves any philosophical problems, or that they now understand the universe wholly. I’ve never heard anyone talking about it claim that they know who/what is behind the simulation.
So IMO the distinction between the two couldn’t be more clear.
I imagine there’s at least a couple wacko groups out of there trying to twist simulation theory into a purely religious endeavor, but that wouldn’t represent the mainstream conversation about it.