Thanks for telling me Juaqne, I didn't know that. I have the same thought as Vixx but it seem strange, so i posted to ask. If it's not a bug then it's ok.

Thank you guys. 

I think he/she deliberately attacking you to clear the arena mission for daily quest without having to lose arena points against another ppl.

After losing twice to the same player, subsequent losses to that player will not decrease your point. Though that one is a hard *** to keep fighting you lol