How is emacs more extensible than vscode when vscode is an electron app in which you're free to do anything a webpage might? I struggle to think of any thing emacs or its plugins can do that vscode extensions can't, and I'd be willing to bet that the extensions are already available and not "you could do it with dev time"
I think parent poster refers to emacs being essentially a lisp interpreter, plus lisp itself being a literal AST spit out, enabling all kinds of extensibility
With VSCode, you've got your settings, and you've got the extensions you can install. With Emacs, the line between "plugin" and "configuration" is more blurred; you can write your own commands to cover how you do your work. -- It's more likely that an Emacs user has touched ELisp, than that a VSCode user has extended VSCode.
I recall running into a problem with VSCode extensions where you couldn't ensure one plugin would be loaded before another plugin. (e.g. loading the direnv plugin, before loading some other program which uses the loaded environment).
