That's a hypothetical legal issue, not an actual one. Also, the companies involved in AV1 did their best to avoid that pitfall in development and have also shown a willingness to go after patent trolls who might try to pull something.

That link is confusing, because it's not a license by dav1d creators, but a copy of the official AOMedia license: https://aomedia.org/license/patent-license/

and it's backed by these companies: https://aomedia.org/membership/members/

That's true of every license ever. You can treat it as implied.