ARTICLE 5. FREE KICK CROSSES GOAL LINE
It is a touchback, if a free kick:
is not touched by the receiving team, and the ball touches the ground in the end zone.
straight from NFL regulations website.
This sounds like that kickoff should have been a safety to me.
I’m still confused why that wasn’t the call, also that should have been a Bills TD in the Huston playoff game a few years back 🤬