Given the vast majority the world has been agricultural for that last 100 years, it should be expected that the tiny minority of cenetenarians are survivors of that way of eating. There are roughly 300,000,000 people currently eating the SAD in the USA alone. If there were a alternate sample of meat eaters to draw your number of cenetenarians from, I'd wager they would have a far higher number. Of the current 306,000,000 citizens in the USA there are only 72,000 cenetenarians ( USA pop and cent pop ). From that extremely tiny minority you cherry pick a couple who at some point in their life claim to have engaged in some manner of calorie restriction, low-fat or cleaned up version of the SAD and wrote their life stories as testimonies to their WOE. Of the current 72,000 centenearians probably many thousands were hard drinking smokers who ate plenty of candy bars and were overweight and sedentary for much of their life; What does that prove?
Anyway, we'll never know for sure - but I'm confident that a high fat, meat diet is much healthier than one that substitues meat with plants - and if there were enough people eating that way - the benefits would be statistically obvious as well.

Also, I really think you stress the longevity thing way too much - I've said it before, but I've personally known a centenarian, even they didn't want to be one. It's much better to be vital and healthy until your end, even if you don't make it past some arbitrary age like a century.