Following that story as it happened, it was all on the phone with the phone keyboard and he somehow made multiple good Neovim plugins including that very popular one (which I use in multiple configs).

neovim is probably the only sane way you could code like this on a small screen. everything works pretty much the same way it does on a desktop terminal, the only thing you have to get used to is having so many lines wrapped, and not having quick access to some characters like $ or ^, but they can just be added to the toolbar in termux