I noticed that when you search on Google for example "why are the french so", the suggestions you get are pretty much… stereotypes. So basically the websites asks google for "why are the <insert nationality> so" and "why are <insert nationality> so", filters results, then send them to your browser that displays them on the map.
Also, the website is open source, and here is the code: https://github.com/getkey/stereotype-map
P.S: I'm a student looking for an internship in web development, please send me a mail if interested! (it's in my bio) :-)