Hmm, I can see some potential shortcuts and cheats taken to present what's in here, but what makes you say the clip was pre-rendered?
The developers say it's from realtime demos of Brickadia projects (though don't say what machines, other than that it's a client/server setup; they do list tested hardware in other blogposts.) They also describe in
a ton of detail how they say it works (including integration of some recent PhysX improvements.) It's pretty far out of my understanding, but it seems like a lot of effort to be a dupe. (You'd put much of the same work in to form a pre-rendered project, but a lot of the blog is about the data trees and other "boring" geometry management challenges, not anything special about the physics collision.) They're also clear about removing some of the buzzwords from the project, such as Nanite and Lumen, which this is
not using; also mentions that they had to coldstore Unreal Chaos and put PhysX back into their UE5 project after Epic swapped out the default physics toolset and it wasn't right for what was needed.)
https://brickadia.com/blog/devlog-4/