It's one of many strong links. There's a good summary of all of them here:
http://onlinelibrary.wiley.com/doi/10.1111/j.1399-5448.2007.00280.x/full
Cow's milk is one with strong correlation. Exposure to enteroviruses is another with strong correlation. I wouldn't say that either was the strongest, based on the data available.
In addition, I am very aware of the work of Colin Campbell and how it is held up in the Vegetarian and Vegan community. It is notable for the sins of omission that could be considered on a par with those of Ancel Keys. Likewise, the milk hypothesis is neither proven nor disproven, and has strong correlations both for and against.
So pick your sources and studies carefully and you can make anything a good way to treat diabetes.
Coming back to Type 2 and using the references you have usefully provided, I am guessing that you put forward a vegan or vegetarian diet as your preferred way to deal with the condition, aligned with Barnard's not infamous book? What you'll also find on here is that Low Carb, Higher Fat intervention has proven very successful as a mechanism for putting T2 into remission, as has the Newcastle Diet approach in those who were significantly overweight.
There are multiple ways to treat T2 at a diet level - what's yours?