He's not talking about Arabic speakers, he's talking about people who can read (to some extent) the Arabic script. This would include speakers of Urdu, Western Punjabi, Pashto, Dari, Farsi and many other (smaller) languages. He may also be talking about Muslims who can sound out the Arabic text of the Koran, even if they don't understand it--a skill which, from what I understand, is valued among Muslims.
But the Arabic language is not the only one using Arabic script. Not sure if you can get to 2 billion with Persian et al., but it would definitely increase your count
Many (most?) Muslims will have memorised the first chapter, and probably at least the last three chapters of the Qur'an. Reading isn't a requirement however, many children (Arabs and non-Arabs) will memorise those chapters verbally well before they learn how to read.
Not sure why this is being downvoted - a quick Google search gives me numbers ranging from 250-450 million, and 350 million sits comfortably within that range.
It's possible that the article refers to the number of readers of Arabic script in any language, which I imagine would be a bigger number.
Because it's comparing the wrong numbers. The article specifies what the 2 million refers to:
"Here's a 18 minute video of I talk I gave at XOXO in 2015 that'll teach you more than enough Arabic to not embarrass yourself in front of everyone who can read the Arabic alphabet to some degree. That's about 2 billion people, or 28% of the human population, and they will absolutely notice that you don't know what you're doing and laugh at you in languages you cannot even read."
There are probably 350 million Arabic speakers.