Wah? Crazy. I just emailed Harold McGee (THE Harold McGee) about whether "the bloom" in coffee really is carbon dioxide (rather than just air on the grounds) and he answered me back almost right away!!
the bubbles are indeed CO2, which slowly dissipates from freshly
roasted beans, so that after a week or two the same beans won't bubble
up. If the bubbles were just air entrained during grinding, old beans
would bubble too