Yes. And the commenter is pointing out that if Guix has a bug, and the available fix is via non-free firmware, they will not pull in the fix. Users thus continue to be affected by the bug.

There's no reason a bug fix for a free software needs to be non-free.

They make it sound like they’ve discovered a secret

They make it sound like they're dogmatic about their views, which of exactly what they claim.

I, for contrast, use free software almost exclusively, but I have no moral problems with using proprietary drivers.

Drivers are software too.

Hence "almost".

I think you’re reading further into this than is there.