I agree with AintNoLimit.
From my experience, so many of these guys at 1/2 are so passive and check/cally it's ridiculous and with that board there's no way that guy would raise you without a straight, even a small raise like that.
Truth is, most of 'em don't know bet sizing at all. So the "weak raise" means he's probably got the nuts and in his mind, "that's a big bet".
If he had two pair with this board, he would just call. Though sometimes I've seen them overvalue two pair but in this instance you're looking at a straight from an unknown. The passive calling stations always play their hands faceup.
I don't know how many times when I first started playing seriously, I would call them down and there it is, "the nuts". And then after the hand in my shell of bewilderment I was thinking, "why wasn't this guy sizing his bets larger with the nuts.
Because they're check/cally Monkeymeat!