The writer seems to conflate bilingualism and multilingualism. Nowadays most non-Anglosaxons are bilingual at minimum, I wonder how much it helps to speak three, four, five languages when you stub your toe.
And outside of the west, monolinguism is rare. Speaking two or three languages is the norm for the majority of humans.
Citation?
As knowing a foreign language is the norm outside anglosphere, I'd expect most people to understand bilingualism as simultaneous bilingualism: "Simultaneous bilingualism is a form of bilingualism that takes place when a child becomes bilingual by learning two languages from birth."https://en.wikipedia.org/wiki/Simultaneous_bilingualism
I don't know how many people are simultaneously bilingual rather than learning a second language later on. I'd assume more English speakers are the latter than the former.
I didn't know either but it seems to be common (>25% of world population): "It is estimated that half of the world is functionally bilingual, and the majority of those bilinguals are 'native speakers' of their two languages."