Okay, an update.

Found another panel, and the other half of that extender was hidden away inside. But here seems to be the odd thing - it appears as though they ran a cat5 cable, possibly direct burial, just for the camera system. There is a network switch associated with this extender, but I don’t know if it can be used for his Eero, Apple TV, and other network devices out there. Or is it strictly dedicated to his camera system? I have not seen this setup before.

my confusion stems from seeing the house network run into a box with the camera NVR, and then out to a separate network switch that is dedicated to the cameras alone. From that switch it runs out to the guest house.