Oh wow, okay, that's great news. Could you fix the manual entry then? Because it still says the following (which wasted 2 days work on my end):
Unfortunately at this time Google Play Game Services only work from a web browser. It does not currently work from Crosswalk or any non-browser wrappers like CocoonJS or Ejecta. However it should still work on mobile browsers such as Chrome for Android.
When I read the info relating to phonegap/cordova, I assumed it meant the plugin would work with Phonegap Build (ie., on Android L), but the above lead me, understandably, to believe it didn't work in crosswalk.