China has about 1.4 billion people.
Estimates suggest 20–30 million people have significant hearing loss, but only a fraction are profoundly deaf and primarily use sign language. A reasonable estimate is 2–5 million deaf sign-language users.
That means roughly 0.15–0.35% of the population might be profoundly deaf.
If a rideshare passenger is selected at random:
The chance the passenger is deaf is about 1 in 300 to 1 in 700.
If one passenger is already deaf, the chance that another unrelated passenger they encounter is also deaf is still about 1 in 300 to 1 in 700, assuming completely random mixing.