How can a 2 handed dagger stun lock a havel monster to death?

I was just chilling and collecting weapons on my completionist account. I was maximum soul level in the lower brightstone cove when an arbiter spirit invaded me. He was cosplaying hidie knight, and rolled around non stop a dozen times. Then when I was in a corner, he took his dagger, and hit me over a dozen times with it, each hit doing 200-300 damage. I was wearing some of the best armor in the game, with total defenses being around 1,200 in each stat. with 2,600 HP. So is this actually possible? or was he hacking with infinite stamina and using mundane dagger with all 99 stats?