To that end, I think it's probably a reasonable guess that people who specifically avoid red meat are people who are generally more intentional about their diet and eat healthier.

I'm not a doctor by any means, but I also struggle to imagine what the obvious mechanism would be. The fat may contribute to atherosclerosis, but that's not diabetes. Red meat does tend to be prepared in ways that yield relatively high calories, so it could just be a matter of general obesity as well.

I'd really want to see a calorie-controlled study comparing chicken and red meat, but that's logistically not remotely simple.

Edit: Actually reading the article, I see there's apparently a link between the saturated fat and insulin resistance, but I still wonder to what extent that link simply comes from excessive calories and how problematic it is if your diet isn't excessively caloric. I'm seeing that apparently around 86 percent of people with type 2 diabetes are overweight.