It's been about that size since at least the 1790s. While it would be easy to assume the Haitian Revolution is responsible, this is not the case. Caribbean colonies were primarily used for the production of sugarcane, which is incredibly labor intensive. As a result, the demographics of most Caribbean colonies consisted of a tiny white population ruling over a huge enslaved one. In 1789 (two years before the revolution), the enslaved population was estimated to be ~500,000 along with ~30,000 whites and around the same number of free blacks(pg 325). That's around that 95% figure right there (90% slave 5% free). By comparison, Virigina in 1790 (thanks 1790 US Census) was less than 50% enslaved persons (292,627 of 747,610). After the Revolution, the white population of Haiti dropped to near 0. Many were killed during the uprising, but a significant portion of them became refugees in the American South.

Riccardo Orizio has written an interesting report on the Polish whites living in the mountains. Apparently, these are descendants of Polish troops sent by France to quell the rebellion, who eventually gave up the fight and were accepted by the rebels as part of the community. There are only a few hundreds of them, mostly living in isolated villages and generally not intermarrying much with the rest of the population (although most of them have a degree of African descent). The report is part of a collection on post-colonial white minorities published in Lost White Tribes.

A few managed to stay in Haiti. Living here I visited a small village called court du fair. When I visited the explained that during the revolution the Dutch stayed neutral so they were safe. the town if full of blacks with blue eyes and blond hair.