you are correct. it is based on draft position, whoever drafts last has the number 1 waiver priority. are u sure that it didn't update the waiver priority (ie. the guy who was "1" put in a claim and now he is 12 and you are 1?). or are u sure that there your claim was fully processed, i realized this morning that the claim i did last night did not go through before i exited out of the page.
also, how is he available in your league already? he can't be added in my league until tomorrow??