When Google's Android M was first announced we all assumed that it will be version 6.0 build... as Android 4.3 is Jelly Bean (J), Android 4.4 is KitKat (K) and Android 5.0 - 5.1 is Lollipop (L).
Surprisingly, Android M will have version number 5.2 according to the latest speculations. What we have is a screenshot taken from the new, exclusive to Android M, feature called "demo mode" exclusive only to the 2nd developer preview release,which clears notifications, simulates a full battery, and generally make the UI presentable for snaps.
The important bit here is the clock, it shows 5:20. This is presumably for "Android 5.2" at least provisionally recall that all official Google press images for Nexus phones show the current version of Android in the clock, i.e. 4:40 for Android 4.4, 5:00 for Lollipop, and so on.
Looks like that Google won't be going so far to version 6.0 with this release as the changes are mostly minor and based on the previous Lollipop APIs with no Key major features available.