The author did mention emacs in the previous article where he talked about editors.
> The reason I didn’t stick around Emacs was basically because of its runtime choice, and ultimately, its Lisp ecosystem. The Emacs community is one of the best I have been talking to, and they have really, really talented people working on insanely complex topics, like turning Elisp code into native code (via C), including Emacs itself. But even with all those optimizations, the editor was still feeling too slow, and has a lot of background that you can feel. All the abstraction layers, all the Lisp macros (oh no), etc.