I can't help but think that this was made possible by the complete collapse in common UI standards. 'Apps' have stopped being OS-toolkit apps and moved onto the web, and of course each designer needs to have their own special on-brand widget style. This has leaked onto the few remaining desktop apps: Chrome rejects the standard Mac OS widgets and reimplements everything, from buttons to the print dialog. Spotify does…
This was anticipated and partly avoided by a reasonably large modal which pops up to tell you you’re in full screen mode, and disappears after a few seconds.
Another similar exploit on desktop was to set the cursor of the page to be a very large image which would overlay the browser chrome and put some fake information there.
The issue on mobile could perhaps be reduced by having some amount of ui that doesn’t go away (safari does this in portrait mode). Another help could be to not make the ui disappear (or make it reappear) when this kind of scrolling an iframe situation arises