That is a wild claim
It is not.
The vast majority of English speakers do not live in the US or the UK. English is the most widely spoken language in the world. If you are at dinner with people from several countries, the "Lingua Franca" will almost certainly be English.
The popularity of Mandarin relies on the sheer mass of native speakers in China. That population is shrinking and that shrinking is expected to accelerate. The cultural export of China is inherently limited by its ideology - there's a reason we have (had, really) "Hong Kong Cinema" not "Peking Cinema".
All Japanese people learn English at school; few learn Chinese as you can verify by reading about the Japanese school system from various sources including Wikipedia.
Similarly in China, English is the only mandatory foreign language taught at school.
Frequently, Chinese or Japanese. For example companies in these countries employ translators. Are you suggesting they rely on primary school-level English to negotiate?
[0] https://en.wikipedia.org/wiki/English-language_education_in_...
> The following is the set of compulsory subjects currently taught in the Japanese education system from the primary to secondary levels:
> * Foreign languages: English (rarely: Korean, Spanish, Arabic, French, German, or Chinese)
That is to say, I would not be surprised if, in China, people are quiet fluent in English.