I am not fully aware of how the program / tool works so don’t take this as a conclusive and fully factual statement. But, no, a specialized runtime is not the same as a modified client. A runtime is an environment where a program or script runs. It interprets and executes your application as had been designed to work. A specialized runtime is a custom / tailored environment that’s built to support a specific set of tasks, applications, or workflows. In this case, the application this one is built to support is getting the Android version to work on Linux.
(Assumption): This is possible because, as some may now, Android and Linux have the same kernel under the hood. The differences come from how Linux and Android built ontop of this kernel. So it’s likely this tool is taking those similarities to advantage (which is why it’s doing it with specifically the Android app, not the desktop apps from Windows or MacOS.)