If you read Guns, Germs, and Steel by Jared Diamond, you'll see that she's largely right. The UK's wealth, and that of most of Europe, is down to being part of an east-west oriented temperate land mass, with plenty of rivers and mountains to act as natural boundaries between different groups of people and so form competing nation-states.
- The temperate climate makes it easy to farm and travel for trading.
- The rivers make it easy to travel inland and trade.
- Agricultural techniques can be spread between people and will apply across the entire land mass, meaning progress is faster because wisdom is shared.
- Anyone with an idea or invention who gets shot down in their own country can go to any of many neighbouring countries to try to get financial backing.
- Regular warfare between neighbouring states forces technological development.
By contrast, travel through Africa and Americas, both north-south land masses, is hard because of deserts and jungles in the way. Agricultural techniques developed in Egypt couldn't be spread to South Africa because of the Sahara being in the way.
China has for most of its history been a single empire covering an area that you could fit multiple European countries into. If the Emperor says "no" to funding your sailing trip to see what's on the other side of the ocean, or, as happened, outlaws such trips, you can't go, end of story. Columbus got rejected by multiple European monarchs for his big trip across the Atlantic before one said "yes" and it was only because he had multiple nations to pitch to that he could keep on pitching.
Intercontinental colonialism is recent history. British wealth goes back long before that. Yes, intercontinental colonialism has contributed to our wealth, but it is by no means the biggest contributor.