I'd like to read about this, do you still have the intended link?
If somebody claims that a vegan diet is healthier and better, I would expect some facts that support that claim at least. Do you know somebody that became centenary following a strict vegan diet? I think that we can discard directly all historical data of "vegan" people living before 1945 or so, because some vitamins weren't still industrially synthesized. This people either faked their veganism or were really very ill. History after 1945 is relatively well documented; thus should be possible to find inspiring stories about actual vegan people living until 100 Yo.
On the other hand, reaching 100 years with a mediterranean diet or a Japanese diet based in marine food has been proved as uncommon, but perfectly possible, with dozens of cases reported at least.
Some interesting studies about vegan diet and it's impact on health:
http://ajcn.nutrition.org/content/89/5/1627S.fullhttp://onlinelibrary.wiley.com/doi/10.1038/oby.2007.270/fullhttp://www.bmj.com/content/293/6560/1468http://onlinelibrary.wiley.com/doi/10.1002/1097-0142(1989080...
All these studies contain findings that support the idea of vegan diet being one of the healthiest option: vegans tend to have lower BMI, blood pressure and reduced (prostate) cancer rate.