I bet the source code of release PF:K could make grown programmers cry.
I also bet the source code of the patched version could make grown programmers jump from a bridge.
Reading it shall become the hot wings challenge of inclined coders.
That's probably true for all games. And Unity is a mess per default.
Yeah, there are many things combined here (no order of importance here).
1. Russians. I do not usually like stereotypes, but in 10+ years of programming I have met exactly 0 Russians who do not code by the "job security through obscurity" principle. It's usually very hard to read spaghetti code. I have no idea why it is like that.
2. Unity. Engines generally invite to write messy code. IMO, it is easier to keep code clean if you control the entire code yourselves.
3. Obviously made in a rush or turned into a rush.
4. Made worse by frantic patching.
Some guy here or on reddit claimed that he has seen pathfinder: kingmaker source code and what it was really good and competently made (I believe it was even before kickstarter).
It's a unity game anyway. I think you anyone can decompile it and see for themselves.
Projects usually start out looking fine. Then come more developers, time gets short. Even under good circumstances, project code only gets worse, not better. It only improves when there is time (so, very rarely) for refactoring.
I doubt you can get the original source code via decompiling. You'd need original variable&function names, comments, etc. - while these are optional for the code to function, they are mandatory for anyone to work with the code.