67s or the likes makes sense. I think he hit his flush but is scared of a boat so he makes a 1/3 pot bet. He can safely fold if you raise big. He figures two pair may call a small bet. So, it's not a bad bet by him. You could get him to fold if you jack it up but I don't think it's worth it especially with the slightest chance he has a boat. I hate folding here but calling sucks too. Since you beat few hands - fold.