The GP commenter makes it clear that the CSV file is written to on the server-side (using PHP) as a consequence of request handling, not on the client side. There is no place that the CSV URL is visible, other than in the PHP source (that clients cannot access) and in the Google Sheet (which is presumably internal to the GP's GSuite domain.)
It's security-by-obscurity, maybe (as all public "secret token" URLs are) but it's better than what you're implying.