It sounds like dry rock that is treated with bacteria. This would be close to the "live sand" people buy, but a different process of seeding it.
There are 2 diff sets of "life" on rock: bacteria, and relatively larger critters. For bacteria, there are many ways to get your population established, aka cycle the tank. Some like to go natural and wait for bacteria from the air, some add bottle of liquid to seed it, some buy live sand, you can buy this rock too. All of those methods have pros and cons.
For larger critters, they will not reanimate after death from dehydration. These are tyour sponges, crabs, snails, filter feeders, etc. Some people like to pay more for live rock that has these to jump start the biodiversity of the tank (not the cycle, though this sort of rock would have bacteria too so it's a 2 birds 1 stone thing), some prefer a finer-grained control over their inhabitants and thus chose dead rock to avoid bad hitchikers.
So it's personal preference. By way of comparison, tampa bay saltwater sells super live rock covered in critters and bacteria, shipped wet. It's basically a chunk of Walt Smith rock that's sat in the ocean. Idont think it's much more that $6 a pound after shipping. Reefcleaners has dead dry rock for $2 a pound free shipping. You can save some $ by using mostly dry with a few pieces of live as seed. If I was going to fill a tank with $6 a pound rock, I'd want some critters on it, otherwise I'd just get dry rock for $2 and a $4 bottle of biospira to seed the bacteria.
