Thank you for adventuring in the halls,
Boundbeasts have been known to occasionally wander into taverns, These are Monsters that yielded to a greater force and learned to fight alongside their comrades, There's also an opportunity one will follow you back from a delve, Both are by design and are only mentioned as enemies on the compendium so that the moment you find or recruit you it feels a little bit more special,
So by design and there's a couple of other little things like this throughout the game you have something unexpected happen and hopefully something that adds a bit more story to your game, Hopefully that makes some sense!
One of the aims over time is to build out the world and the lore, Make the realm and the stories that exist in it feel more alive.