Hi Mc1988,
This is interesting. I haven't had a chance to read the paper yet, but here are some initial thoughts.
Assuming a normal distribution with a mean of 300 and stdev of 233, the Judge is correct, it is almost certain that at least one individual has triglycerides > 500. I could calculate this formally, but it is essentially a certainty.
Looking at the graphs below, it's curious that none of the 25 individuals have tg > 500 and they seem to be much more tightly distributed than the reported StDv, and the mean seems to be slightly less than 300 in this population. Of course, as you note, there were 28 individuals in the population. My interpretation would be that there were three outliers in the population that had VERY high triglycerides, which shifted the mean to the right and led to the higher st. dev. I would say that is likely the explanation, and supports the conclusion that there is at least one individual with >500 tgs.