Correct.
Even though I doubt that there will be more Google Play updates to 1.5.0 (latest is 1.5.0.19), I do get bug reports from time to time and fix them, and send new builds to those users. Those builds have minimal changes just to fix whatever issue that particular user reported (and I fixed). I also post those builds here (what the hell, why not).
There is a separate branch of source code where I work on 1.5.1, and I posted the first (and so far the only) build from that branch. For example, Android Wear support (for which I got zero feedback so far -- does anyone here have one?). The next build from this branch, let's say "-dev2", will hit Google Play as a "Beta".
So it's just like Microsoft releasing updates to Windows 8.1 and at the same time there is a preview for Windows 10.
Or Android L and Android 4.4 (oh wait, they stopped at 4.4.4).