Demonstratable strength has a lot to do with genetics, just like muscle size. It's things like
leverages, muscle attachements etc. In powerlifting you try to move the weight in the easiest way possible, using your leverages to your advantage. Then you also have neural and psychological factors at play.
But generally speaking, the stronger you get the bigger you get also... but only if you get stronger without changing technique. If you reduce your bench stroke by 4 inches by changing your technique and lift more as a result, of course you don't gain muscle necessarily.