He should have said British because its the capital of more than just England. Its the capital of the UK. Therefore it pulls in people from all over the country.
London also makes it money by being a centre of international trade and has done for centuries, it has always been multicutural.
The majority of the population are UK born, the % of British born in London has only fallen by about 10% since 1991, whilst the % of the population that is white British has fallen by about 14%, White Brits however are still by far the largest ethnic grouping in the city.
"Written by someone who does not understand very much at all."
I understand very clearly. You are trying to make out that a powerful majority are actually an oppressed minority, go read what Umberto Eco would say about that.
English ( actually British) culture is dominant, both in this country, and a major cultural force across the world, yet you are playing this like it is under some kind of siege, it isn't.