Project....Zombie?

Do you mean Zomboid?

If so, Zomboid isn't ... the physics aren't done in Lua.

The base of the game is written in C++, and then certain parts of that are exposed to modders via an API that works with Lua.

https://expertbeacon.com/is-project-zomboid-java/

The physics engine is written in C++.

Because Lua is waaay too slow, and even compiled Java is about 4x as slow as C++.