Uh, yeah. The reason for that is that sickly animals carry parasites. It is logical that we wouldn't want to eat parasite-ridden or diseased animals, because then WE get the parasites. If the animal is not parasite-ridden, there's no good reason to believe it would be unhealthy to eat.
My personal suspicion for the cause is underlying SES factors (wealthy people tend to eat better, fresher food than the poor) as well as the simple issue of dietary selection - people who watch what they eat are also more likely to exercise and generally have healthier habits than those who are willing to eat anything.
There might be some factors which the study is failing to control for, but from the link in the grandparent
Included in the analysis were 448,568 men and women without prevalent cancer, stroke, or myocardial infarction, and with complete information on diet, smoking, physical activity and body mass index
The study seems to control for the more obvious associated factors.
Also, the full text states that the consumption of red meat is associated with an increase in mortality when controlling for the confounders assessed in their study, with processed meat b...
There's a lot of background mess in our mental pictures of the world. We try and be accurate on important issues, but a whole lot of the less important stuff we pick up from the media, the movies, and random impressions. And once these impressions are in our mental pictures, they just don't go away - until we find a fact that causes us to say "huh", and reassess.
Here are three facts that have caused that "huh" in me, recently, and completely rearranged minor parts of my mental map. I'm sharing them here, because that experience is a valuable one.