There are a number of articles about it, like this one: http://www.droid-life.com/2017/03/13/what-is-google-carrier-services-android/. No one is quite sure yet, but it seems like it'll help support RCS (rich texting).
Weird reviews for apps like that are kind of a tradition now. Android System Webview also has some goofy reviews as well.
I think the practice originated with silly exaggerated reviews on Amazon, like for this outlandishly expensive Denon cable: https://www.amazon.com/Denon-AKDL1-...ag=hawk-future-20&ascsubtag=UUacUvbUpU5711499