He says "You, the master of the Knights of Ren?"Has that ever been said it's the past? I think Snoke said something like like "You will lead the Knights of Ren."
Kylo is already a the leader of the Knights. I think it is heavily implied in that shot that that's actually the slaughter of the Jedi Academy. Also, he still had his Kylo mask on there, which was destroyed on the Starkiller. Not saying that he couldn't get a new one, but his face is sliced up by Rey for a reason.
Another intersting thing about the mask that I discussed with a friend: Kylo drops the mask and doesn't bother picking it up again after killing Han. The mask was to something for him to hide behind. After killing his father he has overcome his greatest test, and doesn't need to hide anymore, he has embraced the Dark Side fully. Another reason why he probably won't have a, or not the same mask in the next movie.