> they're using CO2 as a working fluid is an attempt to sound carbon-sequestration-adjacent

Um no, that's unfair. CO2 is an easy engineering choice here. It's easy to compress and decompress, easy to contain, non-flamable, non-corrosive, non-toxic and cheap. It's used in many applications for these reasons.

While CO2 is now a great evil among the laptop class, it has been a miracle substance in engineering for roughly 200 years now.