I'm not familiar with what type of stone that is. Some will show polished surfaces naturally, depending on what mineral it actually is. It does show a ridiculous degree of polish if done by a human. Even if purely natural, if it's that out of place for the site where it was found, it might be a manuport, found, liked, and transported to a camp by a native. Impossible to prove when they are surface finds, and possible manuports are best recognized by the artifact hunter who best knows the site in question.