The client source the documentation refers to is a decompilation of legouniverse.exe. However this is not available anywhere, since the legality of it is not quite clear. The files you see may be artefacts from a decompilation project and don’t seem to be part of the original client. The other files that are in the client folder are not source code, the do however contain some useful assets that help/are necessary in creating the server (e.g. information objects and worlds).
I doubt that these decompilation artefact files will be of that much use, looking into that a bit, we might find some interesting strings that tell us more about the inner workings of LU, but unless you are experienced with bytecode, that won’t lead us much further.