That's only true if all the other physics involved are the same wherever that supernova is; your own link mentions this. We can't prove that's the case since we can't test the individual parts of that theory - it's possible to construct a different set of physics that produces results identical to the physics we're familiar with.

That isn't a particularly fruitful approach since it doesn't permit any real discovery - it's rather brain-in-a-jar - but it is still something you have to assume away.