Sometimes, if a game is good enough or fun enough or memorable enough, people will build it within other games. It's the natural order of the universe. That's why Mario 1-1 shows up everywhere. Games Knowers deal in homage.
Rocket League meets all the criteria. (Good: Check, Fun: Check, Memorable: Check; take it from me, I'm a Rocket League Knower.) That's why someone recreated it in No Man's Sky. It's all in the video that's embedded above.
Of course, the foundation of No Man's Sky's creative mode isn't flexible enough for a faithful recreation of Rocket League. This is Rocket League only in the most basic sense -- cars are clumsily knocking a ball around in hopes it'll trickle into the goal. Still, it's cars and soccer, and those are the two main identifiers of Rocket League.
The irony is kind of great, though. No Man's Sky boast a functionally infinite world full of endless possibilities and discoveries. And instead of concerning himself with that, this guy just built another game that already exists.