I thought there was no open API available to control WD TV Live. There are also some requests for this in the "Live & Live Plus Ideas" category.
So how is this Android remote implemented?
It doesn't appear to be based on any specific homebrew firmware.
It's making use of the DLNA Renderer controls.
That's not really an "API," so to speak... Since it's making use of the DMR functions, it can only do certain tasks.