The LBS may indeed know what he's talking about... but it may not apply to you. What is "proper" cycling position? I would ask him "proper for what?" for maximum efficiency? for minimal back strain?
He seems to assume that nobody in their right mind would keep a higher body position, because he implies that a person would probably want to go back to a lower position, which to me is a clue that he may be locked into "everybody should ride like I do."
Now I want to go out and examine all the bicycling backsides and see if other bikes (besides racing ones) put the legs in front of the crank or not. I think there could be validity to this... I've always felt more efficient on a slight upgrade, and wondered if the different angle - which would be, sending the legs behind the crank with the tilt - was behind that.
Hmmm.... so does he like Joe Breezer bikes, which it would seem throw the legs even further behind the crank?
Anyway... the other thing about LBS dudes is often they don't have the greatest social skills...