I don't understand why they chose to use webgl in the browser versus something like raylib. Like don't get me wrong, it's very cool and it worked so it's tough to fault it, I just don't really understand why they chose three.js and the browser out of all options lol.

well they were using Unreal engine before and it was much slower as indicated. they managed to get what they wanted at 8k/60fps which was also their goal so three.js was right for them?

I'm not saying it was the wrong choice in hindsight but Three.js is not particularly fast either so I'm surprised they managed to get 8k/60 out of it.