Advertised as "open source", violates several key parts of the open source definition. It's really a "look but don't touch" thing.
And you do realise ANY copyleft license (GPL, etc) prevents the creation of nonfree applications using that code? Making the app proprietary (yes, GrayJay counts as proprietary) is completely unnecessary.
I know Rossmann brought up NewPipe fakes on the Play Store as justification, but NewPipe is licensed under the GPL. These fakes were already illegal.