Once the beef has been turned into a hamburger, it's hard to identify the specific animals that went into the hamburger's composition ... if you know what I mean.
That somewhat holds for non web apps but when you have the source it's pretty easy to tell what it was made with. Usually if it's a compile to javascript language like TypeScript or Dart the source is going to look horribly obfuscated. The js on the page is pretty straight forward so I really doubt he used one of those.
Looking at the source it looks like everything is hand rolled except for the jQuery dependency.
Looking at the source it looks like everything is hand rolled except for the jQuery dependency.