Ah, the classic faulty hitbox double ko. To further elaborate, rollers create a small 'patch' of invisible margin when they turn, think of it like a sedan's tail when it drift. That 'patch' covers a little bit more ground than what the roller's did, so you can get a kill from doing a 180 turn.
The amount of glitches one can perform with a roller is amazing. Don't get me started on all the lag splatting one can get. If I had a nickel for every time I've been splatted when I've been like five feet away from the roller I'd be able to match the gross GDP of most small countries.