This is the sort of claim that defies easy verification, for exactly the issue you've identified. What does it mean to be the dominant world power? It's particularly difficult to evaluate for a premodern/pre-industrial revolution context. While there was exchange through various direct and indirect measures, China would not have gone head to head with, say, a European country 500 years ago, and neither were economic statistics kept in any meaningful way. (GDP as a measure of economic output was invented in the 30's. And anyways, pre-industrial revolution, economic growth per capita was near zero everywhere.)

Still, in a number of ways, you can see a lot of truth in the statement, particularly when compared to western attitudes about China from the 19th century up til recent times which viewed China as either a dying, backwards dynasty and compared to China until recently, when it was clearly underdeveloped economically. For starters, Chinese dynasties were by any reasonable measure large. The industrial revolution began during China's Qing dynasty. Look up the extent of the Qing empire at its heigh; it covered all of modern day China and Mongolia, an empire of hundreds of millions of people. The Ming dynasty that preceded it didn't cover Mongolia or the far west, but it was quite sizable itself. Ruling over that much territory is not a simple task; for 2,000 years, a succession of Chinese dynasties maintained highly qualified, highly educated bureaucracies managing large empires. I recently read Mary Beard's book SPQR about the Roman Republic and empire and was struck by her description of how decentralized it all was; Rome in her telling didn't really manage day to day affairs in far flung provinces the way we would expect governments to do so today. I don't know if someone has done a direct comparison, but I would venture that Chinese dynastic rule was much stronger and more centralized than Roman rule.

While it might not make a lot of sense to compare premodern economies on a macro scale, as far as material culture is concerned, China also gives any western country a run for its money. China had the productive capacity/technology for making intricate bronze works/ high quality porcelain/ cheap paper long before any western country. Here is a picture of an intricate, lost-wax bronze piece from the Marquis Yi of Zeng's tomb, a warring states era discovery, dated from 433 BC:

https://depts.washington.edu/chinaciv/archae/2zmqzunp.jpg

It's impressive stuff. China mass produced books by woodblock print hundreds of years before Gutenburg. Chinese porcelain was produced at such high quality and in such quantity that it could find a sizable export market in the west even starting in Ming times. The production technology was unknown in the west.

Anyways, I guess the point is, I don't know about the dominant world power, but by nearly any metric, China certainly was a world power.