The author is Niall Ferguson, so I am guessing that the reason is not ignorance, but prejudice in support of the author's agenda, which in this case is an apologia for Britain's empire.

Ferguson writes good stories but will often bend the truth. For example, in 2009 he wrote in Newsweek about the US administration's economic policies. His facts were mostly made-up. See his takedown by economists, for example:

Krugman, Paul (2 May 2009). "Liquidity preference, loanable funds, and Niall Ferguson (wonkish)". The New York Times.