Correct 100%! His stroke might not be straight because of something fundamental such as grip, stance, or whatever. Maybe I shouldn't of told him to just stroke through the ring alone. Your right about that. But if he figures out why his stroke isn't straight going back to the ring would be a good idea to fine tune his stroke.
When I was younger I set it up and would do it REALLY fast while looking ahead and not focusing on the ring. This helped me with my break.
I would also suggest doing this with your normal stroke while looking ahead and not at the ring. It prepares a guy for when he makes the transition to looking at the object ball last when he pulls the trigger. Alot of beginners aim at the cueball last and when they are told to look at the object ball last they are lost...unless you are good at the ring.