Looks like it may be a feature of the normal/bump map - a special texture that tells lighting where all the shadows are supposed to fall. (It's not like meshes could ever be the detailed without cooking a computer).
Modding normals has been rather awkward for FO4 it seems; perhaps the format that FO4 is using is not something that can be reproduced with the Nvideo tools plugin (which many, if not most, modders use for exporting normals).
Undoubtedly it will be cracked, though. They key part is finding someone willing to do it, especially since normal maps can't be edited easily (regardless of how they appear, they need to be exported a certain way, so they can't be patched over as easily as with a painted texture).