MS updated my Office 365 this week. Do you think they might have included "Get Windows 10" with that update?
Don't know ... but it's possible.
Is there a KB (or any other identifiable/searchable) number associated with the Office 365 update you received? If so, try searching on that number and the phrase: Windows 10 ... so see if anyone else had a similar problem after getting Office 356 updated.
Is Office 365 updated automatically or do you have to click something to get the updates (Sorry for all these questions, I do not have Office 365). Is Office 365 updated via the Windows Update process, or some other process (such as settings within the app itself)? If Office 365 is automatically updated, you may want to find out if there is an option to manually control when the updates are downloaded & installed.
You should probably run the GWX Control Panel after any update from Microsoft.
As far as which KB updates one should install (versus which ones to hide), Woody Leonard's site recommends that update descriptions in the Windows Update list that begin with "Security update for Windows ..." should be installed, but those that begin with "Update for Windows ..." should NOT be installed. In other words, install the KB updates that are for security and do not install the others (i.e., non-security).
I would also recommend to keep updating GWX Control Panel regularly.