It appears they've simply copied one of our IPv4 responses and set their domain to reply with it.
There's nothing bad or really that complex about doing this, anyone with a domain can make it work this way. It's possible they've done it to allow their players to play something else whilst they're doing some maintenance on their end or similar. I'm not in contact with them, so I can only guess for potential reasons.
If you're looking to play on CubeCraft, we strongly reccomend you use our address to avoid any potential issues connecting in the future. (I.e. us changing the IP behind the domain, and them not updating it.)