When I wrote that I didn't know about retaliation clauses in AV1 patent pool license. That said, a huge chunk of patents involved in all MPEG standards (AVC, HEVC, etc.) meant that if you tried to go after them, you might have lost licenses necessary elsewhere, so it's all a question of risk analysis for someone who wants to torpedo AV1 with a patent.

What's wrong is claiming that AV1, VP9, VP8 are "patent-free". They are not.