Github's identification is incorrect, the text is clearly the GPL and not AGPL. My guess is that github does its LICENSE-autodetect thing only on the default branch but displays it everywhere (this probably should be considered a bug?).
Gosh, I'm so sorry for spreading false information. Had that license widget not taken up so much screen real estate one might have had a fighting chance at spotting the error :-(
I dread tracking down which issue in the GitHub org that belongs to