ISSUE: How the workshop works? Please help!

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I'm using wallpaper engine from my main account where I bought it. Recently I logged into one friend's account in order to play another game and he had wallpaper engine as well. The steam instantly started downloading an update (his workshop files) and I got instantly GIGABYTES of anime wallpaper crap. Later when I changed back to my steam, I got his downloaded wallpapers missing and mine wallpapers were missing as well when I was in his account. What the heck is going on? How can I make sure all anime wallpapers I downloaded are completely deleted? I don't see them on my account but they're stored somewhere :(