Weired Darkmoon / Gwyndolin glitch

My character is in the Darkmoon blade covenent. I had the covenent ring equiped and invaded someone in Dark Anor Londo. It showed my blue phantom in the Gwyndolin boss cut scene (like I was going to fight him). Then it said "Master of world challenged area boss. Returning to your world." It also gave me the Gwyndolin trophy and 20,000 souls, but I didn't fight him and I am still in the covenent.

I was wondering if this happened to anyone else.:?:

Also I am gussing this happened because I invaded at the exact moment when the host went through the fog door and the host took out the boss with a very powerfull weapon, but I don't know for certain because I thought this was supposed to be impossible.

I had this happen to me also, got mad because it gave me the trophy and I didn't earn it yet. So I went at that moment and killed him. Felt better with my self.