Can previous windows version restore happen automatically?

I help a friend with her computer, and gave it a good clean up, disk clean, virus and malware scan, privacy scan, emptying histories etc. and installing the Windows Malicious software tool. She had her online banking hacked and the fraud squad wouldn't let her have online banking access until she had the computer cleaned up. It actually seemed very clean to me.
She put it on Sleep overnight, and says that when she opened up in the morning, there was a message saying the previous version of windows was being restored, and it was up to about 71%. She says she then turned it off properly, restarted and it said the same thing. I got her to do another restart. This time, the message was saying that the utility she was trying to use was not available, and to insert a CD or stick with the resource on it. Sorry, she is very vague, which makes it difficult to troubleshoot over the phone! Anyway everything appears to be working now, she got back her normal Windows 10 desktop.
So my question is, did anything I do during clean up possibly trigger a return to Windows 8? (her previous system). Would that be the resource the computer was looking for?
Or is she fibbing when she said she didn't touch anything after I left lol? She's done that before, she tends to get very frustrated and start clicking on things and deleting things all over the place.
TIA

If a cumulative update fails during the update it will restore the previous build of Windows 10 before the cumulative update. Need to run winver and see what exact build she is on. 14393.351 is the most recent build with all cumulative updates installed.

List of cumulative updates and build numbers here:
https://support.microsoft.com/en-us/...update-history

Thanks for that, had been thinking it was trying to go back to 8.1. I will check.

List of cumulative updates and build numbers here:
https://support.microsoft.com/en-us/...update-history[/QUOTE]

Use Winver to see which version she's on. If it's still 1511 then a failed attempt to install the Anniversary Update (1607) would give that 'restoring previous version' message - in that case the 'previous version' would be her existing Windows 10 v. 1511.

Thanks for the replies, I think that what Bree just said, and NavyLCDR, is what has happened. My friend had been keeping her computer on sleep instead of shutting down, and I suspect that when I restarted the system an update that had been waiting for restart did it's thing and caused the error message. The trouble with helping over the phone is you don't see the actual message, and I would swear she said it was going back to Windows 8.1, but I think now that it was doing just as you said, going back to the last updated version of Windows 10 :)
She had been advised to just put it in Sleep mode instead of turning it off, I don't know why . I'm of the opinion that a PC needs to be turned off sometimes at least, to 'clear things' and allow updates that need restarts to complete.
Cheers all.

nimue56 said:

She had been advised to just put it in Sleep mode instead of turning it off, I don't know why . I'm of the opinion that a PC needs to be turned off sometimes at least, to 'clear things' and allow updates that need restarts to complete.
Cheers all.

I absolutely agree. My wife is a big fan of sleep [in more ways than one :)]. I can't tell how many times she has had some minor glitch and my first question is "did you restart the computer?" 99% of the time that has been the fix. And it goes one step deeper if you have Windows fast startup enabled. I'm a firm believer you need to fully restart the computer at least once a week and not just the hybrid power state that fast startup causes. My laptop has an i7 processor with a Sata III controller and SSD - so it's no fast startup enabled and complete power down every time for me. I can live with a 5 second instead of 3 second boot time