That's the only fair way to determine if he owes the money or not.
If it was a statement of fact, that's 1st amendment stuff. Can't make the man pay for exercising his right to free speech. If he was wrong though, that's libelous and he owes that man the 50K.
Yep, to ensure fairness. Also unit of measurement needs to be agreed upon, ambient room temperature at the time of measurement, lighting, allowable focal length on any cameras present, etc.