What the parent likely means is that Lisps, structurally, are akin to the AST many other languages generate as an intermediate step to compilation.

A list of characters (a string) and a list of tokens are drastically different to work with. If you haven't worked with both and want to write programming languages, I would recommend filling the gap of the one you haven't to see/feel the difference.

Beyond the code being a list, Racket's macro system and syntax parse / creation tools are incredibly powerful and come built in where you could spend years in another language just getting the tooling to write a language, let alone writing it.

LISP code is not a list as you know it traditionally. It's made up of cons cells. The code of other languages is not a cons cell, altho it is a list of characters. Very important distinction.