This vastly trivializes the work System76 does for months and sometimes years leading up to a product release. We don't simply take an off-the-shelf product that already exists, throw an OS on it, and sell it.
System76 works with upstream manufacturers (like, yes, Clevo for laptops) to determine what types of products to develop, including their specifications, design, etc. for months up to a release. These products do not exist before we enter into these conversations.
Once that has been determined, designed, and goes into production, we start on firmware. We ensure all components are working together and with the Linux kernel (often requiring changes to the components' low level interactions with the OS, since the upstream components themselves are often manufactured with the assumption they will be used by Windows).
Once that is complete, we test with Ubuntu and Pop!_OS specifically, ensuring the OS is working perfectly with the hardware. If there are any OS-specific changes to be done, we write that behavior into Pop!_OS and/or our "driver" which is preloaded on all machines (and available in any Ubuntu-based distro, Arch, Fedora, etc.), with the intent to upstream that into Ubuntu, GNOME, and/or Linux itself as quickly as possible. When this is more generic like ensuring HiDPI works great out of the box, this actually ends up benefiting competitors like Dell's XPS 13 probably as much as it benefits us, but we put in the effort to file the bugs, track them, write the code, and get it upstreamed.
Once all of that is complete, we finally offer it for purchase and market it with all of our pretty photographs, sales pages, etc.
What ends up happening, then, is Clevo offers a machine with a similar-looking chassis for sale as a barebones laptop. This is the result partially of the decision making System76 has made for what to produce in the first place. These products, however, do not contain any of the firmware or driver work that System76 has invested in. They do benefit from the nice photography and advertising System76 has done, and since they look similar, people assume they're going to get the same machine for cheaper "directly from the manufacturer."
Edit: regardless, this is a bit beside the point of the linked blog post, and is also becoming less and less true as we work on designing and manufacturing our products completely in-house.