Here's why:
* "Popular" is subjective: What does "popular" even mean? Does it mean the most spoken language? The language with the most native speakers? The language used in the most international organizations?
* Mandarin Chinese has more native speakers: With over 1 billion native speakers, Mandarin Chinese has a larger population than English.
* English is widely spoken: English is indeed a global language, used in many countries and organizations, and is considered the "lingua franca" of international communication.
So, it's more accurate to say that English is one of the most widely spoken languages in the world, but Mandarin Chinese has the most native speakers.