You might be interested to read Nutrition and Physical Degeneration by Weston A Price, as a lot of his work explored and compared how much meat/dairy/grain/veg each culture ate and what their health was like. For instance, he found the healthiest were the cultures that ate the most dairy (raw, 'organic' by default of course, full fat, local of course and often fermented) and seafoods, with meat anywhere from a couple times a month to every meal. The least healthy were of course the people that had converted to a processed white flour/sugar diet, and in between were the cultures that relied heavily on grains and veggies with minimal (but still present) meat/dairy.
I personally feel best when I eat meat daily (though not at all meals).
I have been lacto-ovo, vegan, low-fat "politically correct" omnivore, and now meat/egg/dairy heavy Traditional Foods, so I have definitely been able to see how I did on each diet.
Finally, WHAT meat you eat makes a significant difference in the nutrition of it. Organic, pastured/grass-fed, with the fat (for the fat soluble vitamins/activators) and ideally organ meats (I am STILL working on that one after 6 years of TF) are a world different from factory farmed, CAFO (even organic) meats with all the fat removed!
Regarding the order of mortality, keep in mind that "regular meat eaters" are likely to be people eating cheap meat including fast food (with fries, soda, etc) and overall a highly processed diet, smoking was likely higher in that group, too, as well as alcohol consumption. I have no idea what study this was, so I can only guess, but if it was done in the last 30 years or so and in this or another "industrialized" country, I would definitely make the above guess.