Josh waitzkin breaks this down really well in his book the art of learning.

He's a chess champion and push hands champion and discusses how to learn. Basically as you become and expert in something you learn to pay less attention to the surrounding environment and only focus on what matters, which allows you to see it in "slow motion". This applies to chess champions where masters eye movement focuses on a much smaller part of the board than a beginner, and also in push hands or BJJ where experts fighting for a tiny bit of grip change is what matters but a novice might just see the whole body not moving or doing anything that matters.

Very worthwhile read.

Interesting, I wonder if this is the thing that happens to while playing this videogames. At some point after hours (30+) struggling against the same boss,you realize you see everything in slow motion,at that point you know it's the end, you mastered it. I literally say "ok it's done, time to defeat it".

Is this Chi

I always thought of it as muscle memory, the movement becomes so ingrained in your body that you can focus on things at a higher level. Keep going up the levels and at some point everything looks like trivial details

I think Senna biopic mentioned him saying road moves in slow motion when he gets into the groove.

TIL! https://en.wikipedia.org/wiki/Pushing_hands