It's bog standard Google Analytics. And the traffic, as far as I know, is completely legit and above board. One of my posts was shared quite a bit on Twitter and Facebook and that's where the traffic is coming from. The traffic was fairly diversified and I could see people browsing in real time.
I can't think of what could be causing it. Is there anything on the site-side, say ads or widgets, that could theoretically stop Google from being able to log page visits?