This is so true throughout the African continent (don't forget about India), for example, where any country that they were in charge of had increased life expectancy, better sanitation, better education, better governments, much more human rights, etc., etc.
They should be proud of themselves especially when you look at the living conditions in absolutely every country they were chased out of.
I noticed the same thing when I did a paper on African countries back in school. There was a systematic difference between countries that had been British colonies versus the non-British colonies. The colonial institutions provided a foundation that gave lasting benefits. It’s a shame that the colonizers are demonized in such a biased fashion today without recognizing the good impact they had.
By and large, at the end of the imperial era the former British colonies did better than the former colonies of other European states or those few that had not been colonies at all. However, even in the former British experience, the results were uneven. In those ex-colonies like Ghana were the British officials were sent packing fairly soon after independence and the locals took full control, things went to pot very quickly. In other countries like Kenya, where the British administrators were encouraged to remain and continue to run the day-to-day business of the country, they did very well.
To some extent it was that the British ran their colonies better for the benefit of the locals, and to another extent...well, you draw your own conclusions about who was qualified to run a country.
And the reason for that is that the Indians were at the same (or arguably) higher level of civilisation than the Brits when the English first came in the 1600s. This did not change until late 1773 when the British won the battles of Plassey. From that point on, you can also trace the rise of English industrialization and their domination of India -- both happened at the same time. They wrapped up their domination of India by the mid-1800s and then had the Indian Mutiny in 1857. overall their empire there was abotu 120 years at the least and about 250 odd for some places (like the cities of Bombay, Madras and Calcutta they founded).