Heal cancels auto attack tick

Me and friend wanted to rewatch this 2v1 because I canceled a auto. We both discovered the auto that was "canceled" happened the same exact time as i pushed heal, we kept watching it and it seems like the heal canceled the damage tick that was suppose to hit the Rumble. I'm not sure if what I'm reporting was what actually happened but I decided to report it anyway cause this seems pretty game breaking in a competitive game to happen.

The "canceled" auto part begins roughly at 0:10