I've seen villains taking this line at NL5 with overpairs, top pair, under pp, AK, ATC...You can't really fold this against an unknown shortstacker (I assume $4 buyins), you're obviously ahead of this range. If he has AA, JJ or a 6, well... He played badly and was lucky that you had a hand you couldn't fold. Take a note
insta-call.... this is one of those spots where you're losing money in the long run if you fold..to me this plays like he has ace jack and makes a bad call pre-flop...he could make the same play with queens or possibly even with ace king (knowing the standard of play at this level)...if he has jacks or something stupid like ace 6 then its a cooler but by calling you're winning more money in the long run when this situation arises against an unknown villain..