I decided to raise it $40 on top of his $10. He ended up taking forever and going all in for $50 more which I insta-called.
Before he turned over his hand he says "I just don't think you got it, I think you're on the flush-draw."
So apparently to him, it looked more like a bluff when I raise to $50 (total) then if I had shoved for $100 into a pot of $27. That just confuses the $hit out of me - I mean, if I had a set or a big Ace, why would I open shove - wouldn't I play it exactly like I played my 7[s]6[s]?
In the end I think I just gave him to much credit - he's a solid player but he makes really strange plays every now and then for almost no reason whatsover; almost as if he just wants to prove he can make tough calls in marginal situations.
He ended up flipping over A-3 offsuit!

Gotta love the respect I get in this game, considering everyone knows I'm usually one of the tightest guys at the table. Friggin' ridiculous how some people completely ignore your table image to make these calls sometimes - he's got $18 invested and the worst thing I could be holding is the very hand I have - no way I raise him as a shorty with just a flush draw - I've either got a big Ace, a set or a pair and a flush draw.
In the end I rivered the 9[s] and stacked him.