A poll

[Brom]

I misread the OP. I thought the turn sequence went check-bet-call instead of the actual bet-call. Because of my misread I voted fold, but would have voted for a call had I been paying attention.

It looks to me a lot like the SB had a nut flush draw and figured the pot was big enough to take a stab at it on the river (this is the only real way to pull down this pot for him). Another factor would be that I would like to see if this unknown player is actually the tricky river type player. What better time to find out this information on a new player then the first hand you play with him? This is not a bad situation to find out that kind of information as there is also a fairly good chance that you do indeed have the best hand. You only need to have the best hand about 10% of the time to show a profit here.

My answer could have been different depending on whether ot not the UTG player timed out with disconnect protection. I can't see the OP right now but I think it was mentioned that he was folded out.