
Legit Google Play apps getting compromised happens fairly often
You will have a legitimate app - and the rest of the apps from this guy look legit... and then someone emails you saying they'd like to buy your app for [more than you're probably making on it now]. Or would you like to add this totally legit customer engagement framework for [more than you're probably making on it now]? It's happened to me! And he sells it or installs it (I did not). You just usually don't hear about it because it's small apps like this, but if you're watching it's about once a week (of those actually detected, probably a lot more). There was an fairly popular app called CamScanner. And the biggest one that I can think of of was Lavabird's popular 'Barcode Scanner' which had 10M installs. Bus most are like this with under 100K. I guess you're only hearing about this one because instead of just serving up lots of ads like most of them it actually recorded your audio and sent it somewhere.
Part of the problem is that while Apple App store apps have pessimistic permissions to start with and you can have them completely disabled unless you're actually using the app (so they can't do anything weird in the background), Google doesn't want do that in case it hurts ad revenue. It's absolutely possible on Android phones - Cyanogen's Privacy Guard did it. But Google just doesn't care, because infected phones serving up more ads is just more ad money for them.