What makes a 'primary' taste?
Unless they found a taste receptor, it likely is a part of the texture (including heat conductivity, solubility etc.) part of flavor. Spicy heat actually is related to temperature and texture (triggers heat - as in literal heat - receptors, does not trigger injury receptors and/or temperature receptors deeper in tissue, so we will not mistake spicy for actually dangerously hot).

The five/six basic taste system (the sixth being fat, currently being scientifically debated) does not describe flavor completely: It completely ignores the factors of aroma, texture (including how non-flavor ingredients will just mechanically keep most of some flavor compounds from ever getting near your tongue), temperature and their interactions. It assumes that bitterness is one dimensional, which is also debated.

Adstringency is considered a separate taste in some cultures, one could also consider it a textural factor (excites tissue in a certain way, just as capsaicin does).