Yes, this would have been on the return to SFO before SLC. And you appear to have been correctly advised all the way through. You are not the first to be caught out by the non-oneworld codeshare differences (there was a case last week involving VY) and I doubt you will be the last, but it's fairly well known in this forum that non oneworld codeshares can cause these problems. Had it been an AA codeshare on SFO-SLC you would not have got TPs or Avios either. In drawing up codeshares - of which there are dozens - lounge access is just not part of the package that airlines draw up. You were particularly unlucky here since AS is more generous with lounge access than most USA airlines, unfortunately there isn't a lounge at SFO and the previous arrangement with AA at SFO ended on 1 January 2018.