Office 365 unacceptable behaviour

I have Win10 Home machine on which I recently installed Office 2010.
I like this version of Office because it is "buy once, use forewer" license.
For unknown reason, probably during some of the Win updates, there
appeared set of Office 365 installs after couple of weeks, the original
Office 14 (i.e. 2010) has been tampered with, clicking on xls file launched
Excel 2016 that insisted on me signing me in and activate the product.
No, I do not want to activate Office 365, I do not want it occur on my
system at all.
This I consider rather cheeky pushing strategy of unwanted product.
I had to manually unistall Office 365 via Settings, which resulted
in errors in the original Office 2010 installation. These, however, were
automatically repaired by the original installer.
Should I expect similar surprises in the future again?

Sounds like you got some software offering a 365 trial. I don't think you will have ongoing issues with MS doing this.

Well, the PC is relatively new (4 months). The only software doing this I can think of is Windows itself. Or maybe the Office 365 was preinstalled and I did not notice it. But for sure I have been using Office 2010 without problems for couple of months and suddenly clicking on XLS file launched Excel 2016.