Answers are in the link though. Unreal’s physics engine did not meet his expectations so he rolled his own.

Usually they aren’t very good, and proprietary way. This is fully open source and has some really good features like determinism and multi-threaded. It is much more precise and performant as well.

If you check the blog post you can see that the impetus for making this game engine was how buggy Unreal Engine’s “Chaos” physics engine was.

Yep, yep!