What nationality would this make him?

my friend has a confusing background. He was born in england, to english parents, he then lived for like 12 years (or something) in another country. he says he went public school and he lived like a local with his family. he then returned to the uk. he is now 16 and bilingual. he has a english pport, and therefor imguessing all his paperwork is also english. He hates being called english. His actually got into fights over it. Where does this mean he is from? can he claim to be from this othe country? or not? i cant see how he is not english but in his heart he isnt... what is your opinion?