I have little to no Stud 8 or Better experience as well, but does his hand need to have scooping potential in this situation for a call to be justified? He's getting excellent odds on 3rd street, even if his hand doesn't have a whole lot of two way potential. He could backdoor lots of hands (straights, trips, full houses, good lows) which would entitle him to at least half of a multiway pot. If he catches bad on 4th street, he can just muck his hand, otherwise he can see what develops for what will probably be a fairly good price.

Bear in mind I'm a Stud 8 novice, and this is just my interpretation.