I think the SB had a very, very strong range to cold 3bet and then 5bet small, and that he 5bet small to try to make you call.

I would not 4bet a hand such as A3, since you're not going to flop a flush draw very often, and even when you do you're still drawing, you don't have a made hand. Another reason is that you're going to be drawn in if you hit two pair with your hand,(or even a pair if you can't get away from it), and that you,re going to be in a situation of reverse implied odds the majority of the time.

I wouldn't call the small 5bet for the same reason. He's 5betting small to try to lure you in IMO, and to make you think you have fold equity.

I think his range is something like KK+. and maybe QQ+, AKs if he's a little bit looser than I imagine.

agree with hubris beside the fact that rag suited A combos are ok to 4bet bluff in general (due to blockers and esp given these positions)...But regarding on reverse implied odds I would still fold vs the 5bet

Range is probably KK + if not just AA - lots of min 5b's seem to be AA lol (plus i think AK people who do this are still worried about postflop with AK so just jam it in)