With all due respect to your esteemed instructor, this is utter balls.
First point is that the aerodynamic stall, and the piloting stall are NOT the same thing. The stuff learned in GS or aerodynamics class is absolutely true about boundary separation at the trailing edge - IN A WIND TUNNEL. From a pilots point of view, the stall is the point where the aircraft does something the pilot didn't command (or fails to do something he did).
To quote a convenient airworthiness standard holding up a table-leg "a stall results as evidenced by a downward pitching motion or downward pitching and rolling motion not immediately controllable to until the longitudinal control reaches the stop" [BCAR S201(a), but JAR-VLA, 22, and 23 use pretty much the same wording I'm certain.]
In something like a Pitts, you've probably got so much elevator authority that the aerodynamic and piloting stall are the same. In plenty of aircraft there is insufficient elevator authority (the CFM Shadow is a classic) to reach an aerodynamic stall and what you get is the classic "mush stall" with the stick on the backstop and the aircraft developing a gentle rate of descent.
But with a reversible control system (e.g. any light aircraft)the elevator authority is a function of CG position, so the stick position to reach the aerodynamic stall on your Pitts will be further back at a further forward CG and visa-versa. I've flown aircraft where at fwd CG you can't reach an aerodynamic stall and only get the "mush", but at aft CG you can get a good solid pitch break, indicative of aerodynamic stall.
For a given wing configuration (i.e.flaps, slats, etc. left alone) an aircraft will always stall at the same AoA regardless of weight and speed, but not at the same stick position. Change the flap / slat settings and the stalling AoA will change too.
I can see however how this could be concluded on the Pitts, it works in a very narrow CG range and has a very powerful elevator - so the stick position to stall probably is damned nigh constant. This is not the case for all aircraft, and only an illusion on the Pitts.
You might like to post the question on the test flying forum, there are one or two people populating that who have done a lot more stall testing than me and might give a different perspective.
G