I am in the lighting business, and DMX is really it as far as low-level lighting protocols in common usage that can do a reasonably high channel count/refresh rate. There are other protocols in the architectural/building automation world, but AFAIK they tend to be fewer channels and/or lower refresh rate. Certainly in the entertainment lighting world DMX is the only low-level protocol in common use, but there are more options in network protocols. For open standards you have sACN (ANSI E1.17/E1.31) and Art-Net (privately developed, but royalty-free and openly documented). Just about every lighting control manufacturer also has their own network protocol, mainly used for sharing show file data between control consoles/NPUs, but some of them can also be used to transport DMX data to and from DMX I/O nodes.
Again, it is possible they're using something else, but I'm not aware of any other off-the-shelf solutions. Even if you were doing something from scratch for whatever reason, the same topology makes a lot of sense--IP network for large-scale distribution, and somewhere closer to the fixtures convert to something (probably RS485-based or similar) that's cheap and easy to implement on the thousands of small MCUs you need to run all of those LEDs.
If any part of the system is fully custom, I would guess that the fixtures are, if only because they need to be architecturally appropriate, but there are some off-the-shelf solutions that could be used as well. It really depends on the kind of effect you're after, the architectural considerations, environment, etc.