I am running Windows 10. Latest version. We have a computer at our construction site. Dual monitor, Display Fusion. I have the same at home.
Often the site computer does not get turned on. The superintendent uses his laptop. Today he turned on the desktop computer. When I turned on my desktop at home it had the wallpaper on the two monitors from the site computer.
How does Display Fusion know about the site computer? Is there a cloud-based server somewhere that syncs the two computers?
I clicked on the DisplayFusion icon in the tool bar hidden icons and hit "Apply" to get back my home wallpaper, but I am confused how this all happened.
Any insights much appreciated. !

Its a Windows thing and proberly because you have your computers sync'd via one Microsoft account. By that I mean are you using the same Microsoft account to login to both computers? If you are then you can easily un-sync the theme by opening the settings app (Winkey+i). Click on accounts then in the lefthand pane click on Syncronize Your Settings (I think its called that in English).
Now click the slider next to Themes to turn it off. That should stop your desktops from changing through your account settings.