“Therefore, we can see Git ignores .gitignore because its in .gitignore, which means it didn’t ignore .gitignore for instructions.”
Put .gitignore in .gitignore and Git does exactly what you told it to. That is the whole post, and it is a joke. Readers on Hacker News and Reddit took it literally and explained Git to him anyway. The post is about Git. The replies are about the internet.