I'm not sure if Kostya's account is truthful. He has a huge axe to grind against ffmpeg https://blog.pkh.me/p/13-the-ffmpeg-libav-situation.html
IIRC, his "LibAV" fork was malicious and his people lied a lot to the community ("ffmpeg is now deprecated!"). Ultimately, they failed, but I see a lot of their rhetoric and resentment in Kostya's post today.
This isn't my place to argue, and certainly he was involved at the time, but LibAV wasn't really "his fork". Reading the full list of names who signed off https://lwn.net/Articles/423703/ I'm more interested in some other names, including darkshikari's deadname and the other heavy hitters of x264.
And if you browse through the ffmpeg mailing list of that historic month https://ffmpeg.org/pipermail/ffmpeg-devel/2011-January/ you'll find his name mostly attached to esoteric video game format patches and not in the big flamewar threads.
Actually - it looks like you can also see in that same month, his post of the first SMUSH codec implementation, that we're discussing in this thread. That's probably a bigger emotional factor than LibAV.