There are dozens of studies that support plant-based diets as reducing all-cause mortality. THIS study is the outlier, and thus demands a pretty high burden of proof.
The only real consistency is that eating loads of processed food (think chips/soda) is strongly correlated with health issues.
Look up Nutrigenomics to understand more, But a great example is changes in the FADS genes and how they impact the intake of long and short chain Omega 3s
https://www.mdpi.com/2072-6643/10/6/758
Unless they are testing people with the same genetics, a meat versus plant diet will continue to result in different outcomes.