Thank you. The implication, then, seems to be that there was an established crop of a Capsicum frutescens peppers in Nagaland, it was crossed with British-introduced Capsicum chinense, and the Naga/Bhut pepper is the result....
I have doubts. I don't know how much earlier the C. frutescens variey was established in the area. Also, C. frutescens is usually much less hot than superhots. Further, C. frutescens is also introduced from South America, thus wouldn't have preceded the C. chinense introduction to the area by more than a century or two.
Could there have been some non-Capsicum source of pungent fruit that were used in the Nagaland peoples'ritual preparation of heads -- perhaps black pepper? The berries of black pepper are red, and the berries of some related species are elongate shapes -- resembling the typical fruit of C. frutescens. Any historical records that you have accessed may have data skewed by names like "pepper", which can refer to genus Piper (to which black pepper belongs), genus Capsicum, or other pungent fruit.
I lack sufficient info to offer conclusions, but these questions come to mind.