I've created a few items and monsters for my ongoing campaign, but have not published them.  

One has three views and the other has one.  

I just learned that having them in your collection makes them searchable by people in my campaign.

So, is one of my players looking at stuff I didn't know I was sharing, or is there another explanation, like Moderators viewing?

Everytime you look at the item it counts as a view, so that might be it. You can also ask your players if they are looking at it and request they don't if you don't want them to. If you don't trust your players that is a completely different issue and that conversation would be better served in the General Discussion are of the forum.

If you “remove from collection” any of your homebrews that you don’t want them to be able to see, then they won’t be able to see them. Those homebrews you create will remain in your “creations.”

You can then add them to your collection, add them to an encounter in the encounter builder and save it, then remove them from your collection again. That monster will stay in that encounter ready to go, but nobody will be able to find your monster until you add it back into your collection again.

I created a test monster and had a friend in my campaign search for it, he couldn't find it.
can players in your campaign even see monsters I haven't published? or is it only items and spells?

They can’t search for it normally, but they might come across it if they brows monsters in the ”extras” section of their character sheets.

But that wouldn’t change their “viewed” count. That was probably you looking at your own stuff.

thank you!