Apple TV Photos - Activity shows one photo

I have Home Sharing enabled on my computer, and if I go to the Computers app on my new Apple TV, I can see all the photos and albums in my library. But if I go to the Photos app, I see only 1 photo.

So I went back to the computer, looked in Photos, and noticed in the sidebar a group called "Activity" under "Shared". That's where the one photo I saw on Apple TV was stored.

Am I correct, then, in assuming that the Photos app on Apple TV shows only the content of the Activity folder in Photos on my computer?

And if so, how do I get all my photos in there? What is "Activity" for, anyway?