You may want to read past that part. The author was just pointing out that only around DMD 2.067 (that's March 2015 or later) did D finally get a JSON library which did genuinely better than those in dynamic language stdlibs, which hadn't been the case beforehand (the stdlib DMD 2.067 rivaling but not being better than Python's json on the author's system).

That's setup for the reveal of "fast" which not only does better than dynamic language stdlibs and than the previous fastest D library but does better than any other JSON parser.

The point of the historical recap is how fast things improved for the D ecosystem: in 7 months the best-case option went from parsing JSON 2~3 times slower than Ruby to parsing it in half the time of RapidJSON, a 2 orders of magnitude improvement in speed.

This post is about the fast project, which is claimed to beat RapidJson, a very fast C++ json parser.

The fast Python json libraries are all C extensions, though. The only "dynamic" thing they have to do is create the actual Python objects when they're done.