The aluminum oxidized in the acidic Star San. Similar to an anodization process, only without the electrochemical help.
That said, you should be OK. If you've ever sent an aluminum pan through a dish washer, you'll no doubt experienced the same thing. For the few seconds you're using it in the wort, you'll be fine.
Also, for what it's worth, Star San only needs 30s to sanitize. Thus, 30s or a few hours have the same result. So for future uses, just dunk in star san for a minute or so.