From a brief bit of clicking around, the author has: designed several typefaces[1], written a long text on typography[cited previously], and has done enough programming to have developed the publishing framework he uses in his books[2], and to have written another book on a programming topic[3].
While I don't agree with much of this blog post, I certainly think the author has put in enough work to have their work taken seriously in this particular domain, and generally seems like a pretty interesting person.
1. http://practicaltypography.com/equity.html
2. http://docs.racket-lang.org/pollen/
3. http://beautifulracket.com