I doubt it's the same pop-up. This one specifically states: 'Based on your update settings you're scheduled to upgrade on ...'. Just closing the pop-up wouldn't change this fact.
Can't really empathise with people complaining about this.
It started with OK and cancel, then changed to Upgrade Now and Upgrade Later, with the close button being the only way to decline. Now it is being pushed as an automatic upgrade with a deliberately small and unobtrusive cancel link instead of a prominent button. Also, if you are away from your PC, it will happen automatically.
Look at their own UI guidelines: https://msdn.microsoft.com/en-us/library/windows/desktop/dn7...
Dialog boxes always have a Close button.
Don't disable the Close button. Having a Close button helps users stay in control by allowing them to close windows they don't want.
The Close button on the title bar should have the same effect as the Cancel or Close button within the dialog box. Never give it the same effect as OK.
Also, read this: http://blog.ultimateoutsider.com/2015/11/the-gwx-control-pan...
It does seem that, on more than a few occasions, Microsoft has gone out of its way to bypass workarounds people have found that disable the GWX app, from resetting registry settings to re-releasing KBs that were explicitly declined and hidden by users.