There is a big section on british citizenship & a section for applying for it if under 18, theres a lot more criteria governing this area as a raft of ammendments have been made to the original relevant legislation.
My understanding with regards to citizenship is that it would automatically be passed on one generation if born abroad (by descent).
Then anybody subsequently born abroad below the age of 18 can apply for british citzenship,under certain specific criteria. They would subsequently have to re-apply as an adult.
Think its most likely application was made this way rather than through work/living visa. (which they can also apply for if they have british ancestry, but i think that is if they havent applied for british citizenship)