It’s using PolyMC to launch multiple instances (depending on how many connected controllers there are) and automatically tile them. I would personally suggest using an optimized minecraft build like Fabulously Optimized to minimize any performance hit from having that many players.
“Heads you get left, tails you get right.”
Heads
“Damn it! All I can do with the left side is move! All the buttons are on the right!”
“Thems the rules!”