In the German survival show "7 vs Wild", one of the participants opened a coconut seed to find it filled with something he calls a "cake" (the light-yellowish part in the image below). It seems to be extremely delicious according to his excessive reaction when tasting it the first time. The texture is described as "spongy" on the touch. The taste is said to be the same as a coconut but much more intense. The video sequence in question can be found here. When researching for "coconut cake" I only find recipes for baking, but nothing similar to this coconut seed core at all. What exactly is that, and how can it be obtained?  
The coconut seed -(what is given in question) is actually known as the coconut "apple". It is a sweet, spongy mass (cotyledon) that dissolves and absorbs the endosperm. This happens when the coconut is ready to shoot some leaves out and is an edible, soft predecessor. This part is actually the Coconut Cotyledon which is sometimes called the 'Coconut Embryo' or 'Coconut Apple' and is suspended in germination and is generally eaten raw. 