Can you link to a specific video or post so I have more context? If you are referring to the the Handmade Hero video archive, then the older videos he uses Emacs, and on the newer videos he is using 4Coder...
Because this is not posted in HH forum, I assume this question is not exclusively about HH?
People here use very many tools/programs to write code in. There are of course emacs and 4coder, but people also use vim, Visual Studio, Sublime, Qt Creator and many many other tools.