China to Taiwan is about 100 miles. That’s quite a swim. I’d call it unusual.
From the Fujian coast? My map doesn’t have the scale notation.
But Cuba to Miami is 90 miles, yet thousands have made that trek in leaky rafts, which is comparable at least to my friend’s midnight swim. Plenty of people do escape to Taiwan from the mainland, though I don’t know whether by boat or swimming, or how many die en route or are caught. The urge to escape communist regimes is hardly unusual.
Satellite view shows about 200 kilometers from Xiamen to Yunlin County, with the island of Penghu County 50 kilometers off the coast of Taiwan, affording a possible refuge for weary swimmers. Penghu went to Taiwan as of 1945. Alternatively, you have a straight 200 klik swim from Qianhai Peninsula on the Mainland to Taichung City in Taiwan.