You don't need a leak to see that, this is how all game engines are built and that's been the case for quite a long time, you have some scripting language that is then compiled by the game engine quite often it just turns your scripts into C++ code and then your compiler takes over.
You can see this with UnrealScript for example.
It's pretty clear why this is done, most game designers aren't experienced programmers and there is a very large push to simplify game development in both the code that needs to be written and allowing a lot of development to be done with visual editors.
If you want to add a new shader it's much easier to develop a shader generator and expose your internal engine functionality via DSL or a UI elements than teach everyone on the dev team how to write shaders, especially since your engine might need to support multiple platforms, so you have a compiler that can target different hardware/software platforms.
Same goes for every other aspect of game development like game mechanics, AI and physics.
So you end up having a small core team of engine and tool programmers and then 100's of game designers that can then work on a higher level.
And it's not that games are unique, this is how computer programming always worked, the core of C e.g. something like printf has to be written in assembly, same goes for your core C compiler (yes now you can technically write a compiler for C in any language including C but when you start from scratch you need to bootstrap it with something).
In fact this is how the web itself works, we have a core "engine" - the browser and DSL - JavaScript and HTML.