Well here is my experience from yesterday. I was tasked with upgrading a PC form WIN XP to WIN 10. As a result of a number of issues, the easiest route was to first restore the original OS on the laptop ( it was a Win 7 machine - then replaced with WIN XP at some stage.)
This is what happened. restored Win 7, waited for process to complete. Almost immediately a WIN 7 "update" showed up. I had no intention of updating win 7, because in any case it would be replaced with WIN 10, But the phone rang and I got involved in another issue.
When I returned to the PC, the WIN 7 update had completed. At some stage I saw the PC asked for a restart but was not paying full attention and just clicked yes. I again came in to see the counter you are talking about running with 10 seconds left and there it was, the WIN 10 upgrade had started automatically!
So what looks like is that a WIN 7 update took place ( Why not after all, you want to keep your WIN 7 up to date not so?) Hidden in that update (just like with the IE 11 one) there must have been this little trick which then started the update without your bookkeeper being any the wiser or responsible for triggering it. Yes these really unacceptable things MS are doing are the problem not WIN 10 per se.
It seems that what has happened is that MS has moved Win 10 from "Optional" to "Recommended" in updates and most PC's are by default set to always install anything in "Recommended".