Both actions change the effective angle between the wing and stabilizer.

You need to understand that the effective angle of attack for a wing or stabilizer is the line from the leading edge to the trailing edge. So when you deflect the control surface that centerline also changes it's angle. In effect the movement of the surface adds camber to the airfoil section AND changes it's angle to the air all at the same time.

We get used to measuring the wing and stabilizer angles with reference to a center line. For example we set the wing for +2 and the stabilizer at -1 or somesuch. In truth the air does not see any stinkin' centerline. The air ONLY cares about the angle between the wing and the stabilizer. So the AIR sees a 3 degree difference at the stabilizer. The true angles of the airflow at the wing and tail will vary widely depending on the flying speed but whenever the controls are at neutral the air will see a 3 degree difference between the surfaces and the model will fly based on that. This difference angle is known as decalage. And yes it is French in origin.

But when you use the controls to change the effective angle of either surface you change the decalage angle. And as you well know if you shim the wing or tail to change the angle the model flies differently. Adding down elevator is like shimming the stab to a negative angle and this makes the decalage angle go more negative and the model responds by nosing down. Adding down flap is the same as shimming the wing to a more positive angle and the decalage goes more positive so the model noses up.