User blog comment:FairyRaven/Fairy Tail Chapter 314: Erza vs. Kagura, Review and Commentary/@comment-24.87.61.44-20130112035721/@comment-5268982-20130112120052

You got that right. "Mashima's favorite armor is plot armor." Still, I think it would be nice of her to lose once in a while...she rarely does anyway. We saw the extent of her powers in the 100 monster battle, so it would be alright for her to lose now. So yes, I think the blood is from Erza too.