[GAMEPLAY] Amumu Q stun proc-ing but not dashing towards enemy

On Amumu, I have landed a Q (Bandage Toss) on an enemy Lux with no Banshees Veil or Spell shields, The stun and damage did proc although I did not dash towards the enemy Lux. The enemy Lux placed a control ward at the same time I landed my Bandage Toss if that is relevant.

1. Land Bandage Toss
2. No Dash

This is the first time I have experienced this bug. Video