Even if you know for sure he only has sets an overpair or the nut straight you still have the right pot odds
to call here, you can even raise the turn and still have the odds if I'm not mistaken. Remember the results of a particular hand don't matter, only if the way you played a certain situation will show a profit or a loss in the long run. This line will definitely show a profit.
I don't know how people play LHE $50NL but I think it's pretty safe to add KQ to his range as well, maybe even AQ, KJ, KT etc. seeing he's an unknown? Again I don't know how loose people can get at limit holdem at those stakes, you should though.