Stiles moved from New York to Beacon Hills after he saw some hunters lurking around the area.
His presence confuses the pack. He smells like a Were, but not a wolf?
Of course, Stiles try to avoid them at all cost, he doesn't want the knowledge that there's a werecheetah, an endangered species, residing in the small town, he is being hunted after all.
Of course Peter finds out. And of course, the pack does too.