A question about a weapon slight spoiler

So I just fought a pvp battle against a guy dual wielding hidden blades-like weapons. Im yet to see them, but thats not the problem.

The problem is that I heard myself getting damaged every time he attacked me, but attacks didn't seem to do any damage. After the battle I noticed how I lost maybe 50 hp as my hp bar was not filled, that was after 10~ attacks from him. I killed him just after he took his two handed weapon.

I wanted to ask if it was just a bug or those weapons are some kind of shit tier?