I assume it’s a search and rescue dog with a microphone. It found the hostages and they told it they had snuck out, hoping the army would be on the lookout for them, but either nobody listened to the recording or nobody gave a shit about rescuing hostages.
They probably figure it’s extremely unlikely to come up. Unless you have:
Nobody would likely challenge it.
This is good, I’m thinking maybe there are doors that send them back to the start that are marked subtly on the map but look normal in the dungeon so they’ll have to work together to figure out why they keep getting sent back to the start and which doors are safe.