It could be that they mean they need a lot of room. Perhaps “inside” is to dissuade people who simply keep rabbits in a cage (though people also keep rabbits in hutches outside).
Regardless, it is objectively safer for a rabbit indoors, barring any other pets of danger are away and the area is adequately bunny proof.
BB users are majority indoor-only rabbits because it’s safer. There is nothing wrong with supervised time in a controlled outdoor environment to have that natural stimulation though.
I wonder about what sort of indoor lives the person who wrote those descriptions observed for the rabbits in the shelter.
To add, though I’m unsure how you search for it, but there may be foster rabbits that arent housed in physical shelters. For example, the rabbit rescue I volunteer at does not actually have a physical place where all the rabbits are kept. All the rabbits are split among foster parents in the area, in their homes, and we bring them to a rental location for adoption days.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.