Depends how they define "use" - as this article[1] points out "Technically, tons of people use Google+, since logging into it gives you access to Gmail, Google Drive, and all of Google's other apps."

If the numbers there are right and only 4-6 million people are using it as a social network it isn't very surprising that Google would be "giving up on pitching Google+ as a social network"

[1] http://www.businessinsider.com/what-happened-to-google-plus-...