I would tend to agree with you on both . .
. . the "Stan" of origin and that it is named after the vessel it is cooked and served in.
This is not to imply that it is in any way "not authentic", just that its authenticity is Birmingham. The curry cuisine of England is well known to be evolving rapidly away from it's Indian and Pakistani roots to become its own thing.
There is no "authentic" cuisine in India anyway. Cooking there makes liberal, in fact essential use of chilis, bell peppers (capsicum), tomatoes, potatoes and beans brought from Central America, tamerind from Africa and other ingredients from China and Persia.
Particularly in the southwest, Indian cuisine has been transformed by Persia, Portugal (Goa/vindaloo) and England, in the northwest by the Moguls (Muslims), and in the northeast many dishes are of Chinese origin.
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