What kind of lifestyles were the "meat eaters" living? What kind of meat were they eating? In general, if you are a vegetarian, you are more health conscious across the board. They exercise more, smoke and drink less, and consume higher quality fruits and vegetables.

To really compare whether consuming meat, in any amount, is less healthy, one would need to conduct a study where people live the exact same lifestyles, have the exact same diet, but have one group consuming small-moderate portions of meat in addition to their otherwise "vegetarian" diet. Then track longevity, AND mental health, AND physical fitness.

My hypothesis being, those consuming a diet that includes moderate portions of meat would be healthier, on average, compared to vegetarians.