The notification will install Windows whether or not you have administrative privilege.
The notification installs nothing. The Windows Update system that you told to "automatically install recommended updates" does the install. The notification is telling you it has been scheduled to happen and how to stop it.
That notification basically says that you WILL be upgraded unless you take active steps to stop it, administrator or not.
Well, yes. You need to take active steps to change a setting that authorizes automatic installation of recommended upgrades.
Windows is scheduled to be installed and it will install even if you do nothing at all!
I think that's what "automatic" means.
This will happen even with a guest user account!
The nature of the account using the system at the time of upgrade has nothing to do with it happening. The admin account set the upgrade policy. I've had systems reboot after updates while users were in the middle of a computation -- them being logged in and using the system didn't change the admin policy (which got changed right after that.)
Though I suspect you do need administrative privilege to cancel the upgrade...
Yes, you do need admin privileges to change update policy. That's to keep guest users from changing that policy. I LIKE that limitation, because it keeps my users from turning automatic updates back on and getting their systems broken by Microsoft.
You're still stuck in the mode of thinking that Microsoft is doing everything properly
Hardly. I'm stuck in a mode of the admin has some responsibility for the upgrade taking place, and that 'clicking the "x"' isn't causing the upgrade to happen. I've never said that making Windows 10 a recommended update was a good thing, or that Microsoft is not out of line for the measures they are taking to remind people to upgrade. I find it reprehensible that they install an "update" that includes a demon that does nothing but keep reminding me that I can get a free upgrade (GWX), that takes special actions to get rid of. But once I've removed it, it doesn't come back. And it never appears on systems where automatic updates are disabled. And even moreso are the mandatory updates for Windows 10.
or that only idiots can misunderstand a notification designed to fool people,
People who think that clicking 'x' to dismiss a window will change a system policy set by the admin are the foolish ones.
or naively assuming that Windows would never upgrade itself without opt-in permission.
Setting the automated update policy is opt-in permission. And the notification was specifically intended to tell people how to change that permission.
Yes, it is naive to believe that Microsoft would never upgrade something in a way that you didn't like after you give them blanket permission to upgrade anything they want to. It's naive to believe that ANY company or software source won't upgrade things in a way you don't like when you allow them to upgrade things for you. There are too many examples of Android apps that I've stopped updating because the latest versions are unusable, or Android itself, or Firefox on Linux, to ever go back to the trust model of updates. But it is also naive to see a notice of a scheduled upgrade and dismiss it with no action with the expectation that dismissing the notification means stopping the scheduled action.