And that's where it gets complicated.
Don't know what his motives are. Could be something as simple as feeling bad that he didn't treat you well and trying to make amends for that.
Could be that he does have narcissistic traits and is trying to fill that gaping void they have with - you. They really have very little of themselves. They can be your bestie one minute, mirroring all your likes and dislikes but there is a huge, selfish, dark side to all of that. Unfortunately by the time you figure out they are one, you are probably well in to the tale.
I also noticed he didn't just mirror me, also mirrored his Brother, so that's something else to look out for.