Windows 10 spontaneously turn Bitlocker on

I received a call this morning from one of my client back in NY state.
Following a Windows 10 update that was performed during the night, she found here computer locked with the Windows Bitlocker encryption, asking for a recovery key to unlock the computer.
I personally setup the computer, when I sold it about a year ago, and only used an offline account, not a Microsoft account.
I did not setup Bitlocker encryption.
Only Office 365 was installed with her college academic account, she is a teacher.
During a system update, Windows spontaneously decided for no reason to apply the encryption to the drive.
She had no knowledge of the key nor the recovery key.

This is pretty disturbing, in my opinion.

I’m glad that this was not one of the kind, because digging in my forum of experts I have been told that there have been many cases like mine, where Windows take the unasked and unpleasant initiative to encrypt your drive.

Anyway, working from remote, with a different computer of her, I was able to find both the key and the recovery key that had been uploaded during the process to her Mircosoft portal account.

In under the user account, I clicked on devices and found the current device. The Bitlocker key as well as the recovery key were there.