How does Molten-WoW PS work?

I heard Molten-WoW isn't actually a private server... they just added private server on it because it is not the official WoW... and I realized that Molten-WoW is too big of a private server... aren't private servers mostly managed by personal PC's... well this private server has 5 realms (Warsong, Frostwolf, Sargeras, Deathwing, Neltharion)... The other private servers I looked up only have 1 realm. And very limited # of people, features, and connectivity... Molten-WoW has over 50k users...