the thing is, in this hand the SB check/called a bet and a push (albeit a small push), so he either has a really nice hand (ie set/ 2 pr) or a drawing hand. The fact that you bet on the turn leads me to believe you put him on the drawing hand, but then the problem is that you did not bet nearly enough.

If you are unsure here against a loose passive player you might be better off betting the turn harder and checking the river behind.

Against a tight passive player it's probably a check on the turn, then call the small value bet on the river/check behind.