It's kind of like Beauty's mom going out at night, but the difference is Beauty knows his secrets, and his place is with her, not the wild nature he once had.
Oh man, this is like when she watched him go off to hunt at the castle (albeit with a much less bloody ending). Again, I'm glad to see that Argus' time as a beast has left a mark on him--made him inclined, sometimes, to go out at night, if not very far from home. And Beauty looks a lot like her mother here, likely due to the cloak or blanket that she's wearing. They both emerged from the castle changed, but they are better and stronger people for it, ultimately.
