@nemobis actually, i wasn't connected to wifi. i didn't think it was a problem, because lbmk caches everything aggressively, as i'd ensired before the talk.
i overlooked that grub was also downloading PO files for translations during build time, so i got caught out by that. i fixed it, the next day after my talk. see patch:
https://browse.libreboot.org/lbmk.git/commit/?id=8f128e6728e3486fa2c91d4610da3ab3df22249f
i could have improvised during the talk and disabled grub in lbmk, for demo purposes, but oh well. i'll just do another talk to correct the old one