> what Purism is doing is moving the non-auditable part of the OS onto a separate storage device so that they can claim that the OS is "Fully Auditable" and FSF certified even though the non-auditable and non-free part is mounted into the OS filesystem during boot.

Yup, that's part of it.

But remember, even if they didn't do it, there's still a matter of them by using components with internal flash storage for the firmware instead of shipping firmware with the OS and letting the OS upload them. Like that's not a hackjob like the /lib/firmware or /run/firmware stuff or anything, but it's not like it's any more "open" than any other system, if not being a bit more opague. Of course the marketing would still be deceptive then.