Mistakes DO happen, and its fine in hindsight saying what you would and wouldn't do, but its too late. Maybe it was negligent, but no doubt it was not done on purpose and had the pilot in question realised the problem I'm sure he wouldn't have taken off.....Just like NASA or whoever it was who mixed up metric and imperial measurements when they sent a probe to Mars. There is a bit of a difference between fps and m/s, and it caused the probe to burn up......
I was going to write my "fuel story" here, but decided against it for fear of incriminating myself
.....The moral is DONT TRUST THE GUAGES!!! and be extra cautious when calculating endurance in an aircraft you don't know !
Cheers
EA