You can't prove that BTC was mined by satoshi, is important to remember how he wasn't alone in the early days, other users were mining with them.
Another point to think about is, what if the privatekeys from those address was found by brute force, we know there are a lot of users trying to solve the puzzle, and maybe some of them found address with balance while trying to solve it. The odds of this happening are really low, but it's possible.