What you’re seeing there is the application running in a Linux environment (chroot) under the Android OS. It is not native to Android but runs just as well since it is not emulated. There are several methods to have a chroot, pick the one you like the best, but I recommend the Debian way: https://wiki.debian.org/ChrootOnAndroid
The phone is a Motorola MotoG 3rd gen, so quite an old phone with 840 MB memory and 1.2 GHz quad-core CPU. My application uses about 33% of the CPU while idle receiving and the whole Linux chroot uses 180 MB of RAM.
The application is free-software released under GNU GPLv3, see http://qradiolink.org for details and links to code. You should have no issues compiling for ARM under Debian Jessie or Stretch (or in fact any other derivate distros). You can either cross-compile on the host computer or directly on the phone (but will take longer). If you want to help you can try setting up a Travis build to provide binary packages for ARM HL architecture
At some point I plan to release a ready made SD card image with the full GNUradio environment preinstalled, to be plug-n-play.
Oh, and the demo does not contain any reference to video transmission because frankly with the bad lighting and the small size of the screen nothing would have been visible.