@gsuberland Yep, there's been an official behind-the-scenes video on MS blogs at some point.
I think that's gone, at least I can't find it, but if you search "windows 10 wallpaper behind the scenes" on YT you'll find a bunch of really weird reuploads by spammy low-viewer-count channels, some of those containing more of the original vid, some less...
@gsuberland Found those screencaps for now...