I would say that the GUI related to that is sufficiently unclear for making you doing that without wanting it.
Moreover, If it was only me, I would say that I'm too stupid for understanding how it works but this happened to friends of mine also who are way too smart for doing that :)
Unclear?
You have to enter in the setting and click a check box where it it clearly states that the pictures will be backed up.
But you're now changing the goalposts, facts are:
- There is no obligation of having a Google Plus account
- Picture backup is disabled until you opt in
- By default all the picture uploads are private
Moreover, If it was only me, I would say that I'm too stupid for understanding how it works but this happened to friends of mine also who are way too smart for doing that :)