I don't think that's a fair categorisations. I believe that is only for selling steam keys elsewhere.

Steam allows publishers to generate steam keys for their games at no cost. The publisher can then sell those keys elsewhere. The only requirement is the keys not be sold for less than the price charged on steam. ie if the publisher can sell the key on any other platform and valve gets $0.

Expecting valve to distribute your game and provide access to their steam works features for free while allowing a publisher to undercut them would be insanity.

https://partner.steamgames.com/doc/features/keys

Steam Keys are single-use, unique, alphanumeric codes that customers can activate on Steam to add a product license to their account. Steam Keys are a free service we provide to developers as a convenient tool to help you sell your game on other stores and at retail, or provide for free for beta testers or press/influencers. Steam keys are a free service, so we ask you to use good judgment and follow basic guidelines and rules around requesting and selling them.

This is completely incorrect.

The rule is that

You cannot generate Steam codes and sell them on alternative storefronts for less than you would sell them for on Steam for a similar length of time.

There is absolutely no rule saying that you cannot sell your game on alternative store fronts for less. There isn't even a rule saying that you can't sell Steam keys on alternative store fronts for less than you are currently selling them of Steam. Just not always selling Steam keys on alternative store fronts without at least sometimes selling them for that price on Steam.