I didn't know this was a thing until I met my partner, who has it (and so does her mother), but there is a couple conditions called fissured tongue and geographic tongue ( ex. https://en.wikipedia.org/wiki/Fissured_tongue ) which effectively means that her tongue is a lot more sensitive to salt/pepper/spicy than average. To the point where black/white pepper alone might give the same intensity chilli gives to a "normal" person. There are many reasons for the variance.