Nah, that's not it. Try riding a bike in reverse (or pushing it). It's not at all stable, because the feedback is applied in the opposite direction. You'll fall right away, even though the gyroscopic effect is identical.
If it rolls oriented forwards it will stay upright by itself because of the steering.
If it rolls oriented backwards it falls over because the steering now pushes it off balance.
If the gyroscopic force was the most important thing keeping it upright it wouldn't matter which orientation you let it roll.