Tough fold in a Party 30+3

[krammatrix]

704 entered, ~250 left. Avg. is 3k, hero has 4.5k, villain has 2.5k. BB is t150
UTG+1 limps,
Hero limps UTG+1
MP limps
SB folds, BB (villain) checks
Flop: A6h2h (t675)
BB checks, UTG+1 checks, hero bets t250, MP folds, BB calls t250, UTG+1 folds
Turn: A6h2h 7d (t1175)
BB checks, Hero bets t350, BB calls t350
River: As62h 7d Ts
BB bets t1500 (allin), Hero folds

I don't really know about any part in this hand that I did anything right. It looked a lot like a missed flushdraw, because it seemed like a wierd way to play a set/2 pair. I almost insta called because it looked so suspicious, but it would have left me with only t2000 left, and I was still in good shape with the t3500 i was left with after the fold. Is this standard?