From their end, if that was a thing they regularly did, it would be such a hassle. After all, you'd have to find a new person to do that work every time, find a way to split up the work into very small chunks, and who knows if the result from a person off the street would be usable?
My guess would be that he was trying to evaluate how you respond to bug fixes and criticism. (Still sounds like a weird interview strategy though)