Reminds me of the Codeberg/SourceHut DDoS of January last year. CodeBerg even helped out SourceHut by hosting their status page. SourceHut ended up adopting Cloudflare.
If you reread the post mortem you linked, you'll see they reached out to CF for a quote but ultimately ended up not picking them, despite the very generous free offer.
Any reason why they seemingly had and easier time with IPv6? A simple lack of participants in the botnet, or are there some protocol-level tricks going on?