That's right, we have no proof that they're Satoshi's, we don't even know who it is - is it one person or several. We'll probably never know. But these addresses were used in the original mining, and so they're believed to have been generated by a single user because the block reward was 50 bitcoins, and they're multiple addresses with 50 each. We'll probably never know who Satoshi is, so he remains as a mythical figure, and these early addresses were never used anyway.