The potato intrinsically has all the ingredients it needs to form nitrosamines given a high enough cooking temperature. The presence/absence of oil and type of pan are unrelated. Pan fried potatoes produced a greater amount of nitrosamine than deep fried potatoes. Although this study I have referred to didn’t specifically test foil wrapped potatoes on a charcoal grill, I would imagine that these too are laden with nitrosamines. Baked potatoes and boiled potatoes are safe to eat.