As you say, it can be a false perception due to the pitching effect of crow or flap. The primary effect of lowering flap is to make the wing pitch nose down and thus make the model dive, giving the impression that putting the flaps down reduces the lift. Putting ailerons up for crow will make the wing pitch nose up so the plane rotates up and climbs, giving the impression that up aileron increases lift.
Those effects are complicated by other factors though, such as the location of the tailplane in the downwash and the effects of sweep putting the changing lift and pitching forces ahead of or behind the CG. Those effects due to the layout of the plane can make the movement of aileron or flaps have the opposite effect to their pure moment of pitching around the Aerodynamic Centre. Raising ailerons on a swept wing model not only causes nose up pitching around the AC but a downward force behind the CG, so you get a double whammy effect trying to raise the nose and thus compensating for the natural stability that is trying to lower the nose at low speeds. Lowering the flap on the swept wing creates a nose down pitching around the AC but the increased lift well ahead of the CG produces a nose up force and the outcome of that may be a small nose up or down or no net force. So the effects of moving control surfaces around can be quite different simply due to wing sweep, but in general crow will result in less nose down or even a nose up pitching, meaning the pilot is pulling back less on the stick at low speeds, and thus may give some people a false impression that the wing is working better.
H