[KaVir]

It's not really feasible to hand-write millions of individual room descriptions; most likely they're using a wilderness/overland system for the majority of their rooms. In the early 90s such systems usually recycled a small number of static descriptions, or even had no descriptions at all (instead relying solely on ASCII maps for navigation), and they got something of a bad rep. But towards the late 90s there was a push towards dynamically generated descriptions, and over the last decade the quality of such descriptions has improved quite a lot.

I don't know what approach they've used, but as a modern mud I imagine it would have some pretty intricate system for generating descriptions, and of course they could mix in hand-written descriptions for cities and such.