like others said, the turn bet was too weak. im working on this type of leak now - betting "feeler/blocking" bets on the turn with scary boards.

and like you said, the most likely holdings are pair/draw or pure draw - so bet around pot-sized on the turn, then probably check/fold the river if called on the turn...but maybe a 1/4-1/3 pot block bet would be better - id also like to see what others think of the river.

the other option is to check it down after the flop and wait for better opportunities. either way, the turn bet = no good.