I would argue it's not childish and is a strong point considering emacs is not typically installed by default. Vim isn't usually installed by default either, gotta go with good ol' vi, unless your distro maintainers are nice and symlink vim to vi for you until you install vim.

At first I thought the same as you, but then I realised that he's not talking about your average editor, but about which editor to use if you SSH into a random web server etc. The thing you use in a foreign environment. That's what "random Linux editing" probably means.

This. On your home computer, use whatever you want. If you're using all sorts of foreign environments, you're going to want to use whatever is common to all of them so that you don't fumble around badly trying to do basic tasks. Learn vi. You don't have to like it, you don't have to use it on your home system, and you don't have to learn the eleventy-billion vim-efficiency-hacks floating around the Internet. But learn it well enough that if you have to ssh into some server that only has vi installed on it, you aren't rendered completely helpless. Even "Notepad Capability" is fine.