What does "crate trained only" mean?

Yes, Crate trained means that the dogs do sleep in their crate. If you are not familiar with crate training than it may seem harsh but dogs that have been crate trained actually learn to love their crates. It becomes their safe place.

The dog doesn't necessarily have to sleep in their crate. I require crate trained animals so that everyone who is boarding has their own area should it become necessary for safety reasons. I don't leave dogs unattended together, so it allows me peace of mind knowing that I can leave the house for dinner or running errands, and no dog issues will occur while I am gone. But I don't require the dogs to sleep in their crates if they are more comfortable elsewhere.