> the number would plummet precipitously, likely leaving Mandarin at the top

70% of Chinese speak Mandarin as a first language [1].

> the sense of being able to say hello, thank you, and introduce themselves that is probably true

This is English learners. If you count English learners, a third of Chinese speak English and a majority of the internet-connected world.

[1] https://en.wikipedia.org/wiki/Languages_of_China