>Is there some reason Lisp is superior to any other general-purpose programming language for text editing?

purely for text editing? No. But that's not what distinguishes Emacs, it's famously very mediocre at it. The point of Emacs is to be a fully transparent, inspectable, dynamic and changeable environment. In spirit similar to Smalltalk systems like Pharo. And for that a Lisp is not the only choice but a very good one.

There's very few languages and environments that facilitate jumping into any place, making a change, compiling or evaluating a block of code or treating it as data and continuing seamlessly.