Yes, you’re correct about that.
But, think; what’s the goal with relocating WordPress into its own neat little subdirectory, anyway?
What purpose would one possibly have for moving WP down the hierarchy within the webroot… other than the intent to serve other things in the webroot without mixing them up with WP files?
If the goal was simply to only have WordPress and WordPress alone in your webroot - you could pick any arbitrary folder on disk, set the webroot there, and not have to worry about rewriting at all. Things would be much cleaner that way!
You might even pick
/var/www/html as your “arbitrary folder on disk”.
But, no, I have to assume the point of this is neatly sideloading other files, which that rewrite exemption allows for.
P.S. Other than slipstreaming other assets, this also allows the other behaviour specified in the document - that is, installing separate versions in other subdirectories of the web root.
The “default” becomes whichever one you rewrite to, and you can manually select for specific versions by prepending them yourself. That way, if you navigate to a version of the site that actually exists on disk, you get that version, ELSE you get the “default”.
Without this rewrite exemption, this behaviour would break, since you can specify the subdirectory for a given version but the web server would still prepend it with the “default” subdirectory - resulting in a nonexistent URI.