The end user said when he started up his PC Monday morning his computer looked like his old OS....?
There was probably a screen to choose the operating system - a dual boot menu as discussed/shown in this article. I've seen this on only a few Windows 10 computers that have been upgraded from a previous OS. The user chose the wrong one.
"Living tomorrow is everyone's sorrow.
Modern man's daydreams have turned into nightmares."
I don't, however, understand what puts Windows 10 into that mode where it offers to boot to the old O.S. It would be nice if somebody knew the reason that it happens. And it apparently happens rarely because I've only seen it at one company.
But why are you offered the choice when you have upgraded. Most PCs DON'T show the choice after having been upgraded.
I added a delay to mine so I can choose whether to press F8 or not for system diagnostics. If you change the boot up delay, you will see it. Normally there is only a choice of 1 but depending on how you did the upgrade, there is sometimes a choice of two.