Briefed the users? You mean the second graders it played against?
She grew up on a farm in the 1940s, where she got to use potentially lethal machinery as soon as she could reach the controls.
Of course, if a complete manual with all safety information wasn't provided, that's clearly negligent and should be prosecuted to the fullest extent.
It was a 2-stroke Stihl, probably the smallest they made, with an automatic brake in case of kickback. And a manual explaining how to avoid it - I never had any issue because I followed the directions. Including goggles and over the ear hearing protection.
Many people have gotten used to these things having pretty high safety standards. I feel like you can't fault them for not knowing the intricacies of how the designers programmed the robot to handle movement and collisions; it's just not something everyday people will have in mind. And as a parent, you'd assume that the chess tournament wouldn't be putting a machine in the room and allowing children to play if they knew it was dangerous.
I wouldn't be fuming with the chess federation either for not necessarily knowing and thinking about it, but I think their response is a bad look; it came off cold to me and like they were looking out for themselves. At the end of the day, they put it there, allowed the visitors to play against it, and something went wrong. Apologize, look into it, fix the problem, and let insurance pay for the accident. Take care of the person who got hurt in your tournament.