It clearly is a joke. I could see myself making the same joke when I'm in a playful mood. His other sentences are excellent, and he doesn't have other writing e

It clearly is a joke. I could see myself making the same joke when I'm in a playful mood. His other sentences are excellent, and he doesn't have other writing errors (disclaimer: not the best writer myself), that's enough proof for me. Also, he's communicating in a playful way the whole time. As cpfohl said in a similar vein: I think the joke acts as a disqualification for people who don't appreciate it, i.e. acting as a filter.