Luckily took a look and discovered that it is not really about that,
but how to use layering in Caustic to create new instruments as a full on sample instrument. Which of course opens up all kinds of sheenanigans when it comes to textures, experimentations or just to finetune a drum.
If not knowing about this, pay attention. Specially as it is only Caustic that have this function of any apps on Android (and probably on iOS).
Download the instrument being created: