I am just a mod, not even an admin. So, I've not go any clue about infrastructure. Like mentioned, we could probably do some digging and make a few educated guesses. A quick look says they're using different DNS settings, both from CloudFlare. I suppose it could also be a mirrored copy, but that seems a bit excessive and I don't see any redundancy benefits if nobody knows the second domain name.
The good news is that not knowing any of that stuff means I'm not obligated to fix it if/when it breaks!