In my personal experience in AH, if I cause the collision, I get damage. Ok fair enough. If someone collides with me, I get damage. I honestly cannot say I have ever flown away from a collision in the game undamaged. None that I can recall, but hey I don't play a lot anymore.
You maybe just did not notice the 'collisions' that didn't hurt you, because there was none on your side - just on your opponents.
It's all in the messages :
"XY has collided with you"
"You have collided".
If you see the first one, your opponent had a collision on his screen and will take damage (the actual amount can vary a lot, of course).
If you see the second one, you had a collision on YOUR screen and you will take damage.
Often you see both messages, with consequences to both participants.
If there is only the first one, you might not even notice it, because the is no bang and no damage to you, and it's easy to miss a single message during a dogfight. (And people are more inclined to take note of events that hurt them)