Ok, just to make it clear for everybody that is concerned.
SDR Touch DOES NOT
violate the GPL license!
SDR Touch is merely a client for - https://github.com/martinmarinov/rtl_tcp_andro-
. rtl_tcp_andro is released under GPL2+. SDR Touch and rtl_tcp_andro are separate works in the sense of GPL. They are neither statically or dynamically linked and they are two separate executables that communicate over a TCP connection. rtl_tcp_andro is bundled with SDR Touch merely to help the user and with accordance to point 2. of GPL Terms and Conditions. You can think of SDR Tocuh as an "installer" of rtl_tcp_andro. It just launches rtl_tcp_andro with Runtime.exec("");. Furthermore SDR Touch could happily work without the bundled rtl_tcp_andro in network mode by connecting to a remote computer running either rtl_tcp_andro or the original rtl_tcp.
Therefore GPL is not violated. Saying that GPL is violated would be like saying that you can't listen to online radio with your proprietary music player because the radio is being streamed with a GPL based software.
A quote from GPL-3.0:
A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an "aggregate" if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate.