I can’t speak for the judge, but I suspect the argument would be partly around whether or not it was a safe design, including whether there was sufficient ‘redundancy’. This would include whether they’d taken sufficient steps to ensure it was a safe design through risk assessments, testing and compliance with technical standards (In America that’s likely to be ASTM standards).
We know lots of drop towers have seatbelts. Given that the seats on this one tilted, you might argue that the case for having seatbelts was particularly strong here. So I think part of the case would be looking at why there weren’t seatbelts.
Seatbelts could have done two things. Firstly, they could have prevented the restraints opening more than a certain distance, regardless of the sensors. Secondly they could have prevented a rider sliding out, even if the restraints were open ‘too far’.
There probably are arguments both ways, but it says that Fun Time didn’t represent themselves in court and were found guilty in their absence. They didn’t attempt to make a defence so the barrister for the prosecution’s points would have gone unanswered.
I do agree that $310 million does sound like an astonishing amount. It’s likely to reflect the fact that Fun Time didn’t appear in court and don’t appear to have given an apology. Realistically a ride manufacturer isn’t going to have $310 million, so I suspect the judge is effectively blocking them from doing any further business in America.