I made that up, so feel free to take it with a huge grain of salt. But I've worked in higher education, wrote my thesis on it and follow it still with a lot of interest, so the ballpark figure is probably roughly accurate.
I'd like to send you sources but honestly ranking education objectively is tremendously difficult. There are lots of different rankings that measure things you may not, at all, consider to be indicative.
For example, most rankings are heavily weighed towards citations and proxies thereof. e.g. Chomsky is one of the most rated academics ever, so if he moves from MIT to your university, your rankings blow up. Despite the fact he doesn't teach any classes, and the number of typical students that actually benefit from his (previous) research being associated with your university is close to zero. Particularly the type of students we're talking about: those who do a 3 or 4 year bachelor, then go to work. Lots of universities have high rankings because a handful of academic experts in their field are associated to the institution and put out innovative research, which usually means very little to the undergrads's education or development. Look into the methodology, it's usually a bit of a joke. It's the reason universities can rank from 40 to 140 to 40 within a a span of 3 years, despite no student having noticed any difference in the quality of their education. In short, university rankings are more about research than about education, which is fine, but the problem is they're often used by would-be students when choosing where they can get the best education. (or rather, which institution looks best on their resume, I guess). And I'm primarily talking about students who get a degree and then go back to work, those pursuing academic/research careers is another story, but it's a minority the article doesn't really focus on.
But that's just rankings. Even if you had good rankings, just counting the number of universities worldwide is tricky and runs into different ideas of what constitutes a university.
But to give you a sense: if you look at the QS or THE rankings which are quite popular, all universities in the Netherlands rank in the top 300. The US alone has more than 3000 universities, worldwide there are over 25000.
So in short and all honesty: made up the figure, I do think it's roughly accurate, I don't think there's great sources/metrics which reliable rank educational quality worldwide, and the metrics I don't really put much faith in would at least rank the 13 universities we have within the top 5%.