Not all abilities that cause movement in some way shape or form are considered movement abilities, it seems that the classification is tied to moves whose primary purpose involves direct horizontal movement rather than everything that causes movement.
I think the best thing that can be done by Valve is to give a more clear definition of what a movement ability is.
Further Examples: Rake (passive float), Gutshot (knockback), Naptime / Barrage / Storm Cloud (float), Goo Ball, Traveler, Ground Slam, Jump Start / Willpower / Kinetic Carbine / Slither / Kudzu Connection / Rallying Charge / Burrow / Smoke Bomb / Bloodscent / Dazzling Trick (Movement Speed Increases), and Riposte (parry moves you)