The NHS uk page (link below) describes both types of diabetes and is quite vague about the cause of type 2 diabetes, saying it is "often associated with obesity" and goes on to mention diet and lifestyle.
When working as a nurse we were told that a high sugar diet was a predisposition (although this was some 20 years ago and views may have changed). A high sugar diet could of course cause obesity.
It suggests to me that research has still not determined a particular cause but that it is wise to eat a healthy diet, avoid too much sugar, and not become obese. A healthy diet does tend to include low sugar. It did used to be called 'sugar diabetes' by my parents generation. A high carbohydrate diet could also cause an excess of sugar as carbohydrate is broken down into sugars.
The NHS link is here
Diabetes - NHS Choices
Medical News Today reports research that says sugar is the main culprit and not just high calories. So it seems to have gone full circle and come back to a high sugar diet being seen as a prime cause.
High Sugar Consumption Linked To Type 2 Diabetes - Medical News Today
So in terms of whether it is obesity and lifestyle, or high sugar that causes diabetes it seems that both views are correct, but that sugar intake is a significant factor. Certainly in people who already have diabetes, sugar intake needs to be managed - and the theory is that many people develop it gradually or are prediabetic, so don't know they have it. This could also be the case in hamsters, so in breeds of hamsters known to be at risk, it would seem sensible to reduce sugar intake and ensure a balanced diet, especially as they may already have undiagnosed diabetes.
Just to confuse matters, the US National Library of Medicine has published research into diabetes in chinese hamsters, saying that there is a recessive gene causing type 1 diabetes and inbreeding has caused a line of hamsters born with diabetes who have prediabetes. Not all chinese hamsters, just the ones born with the gene, but it does talk about percentages and breeding lines. They say restriction of calories and dietary fat prevented onset of the disease in prediabetics. However it could be that the restriction of calories included low sugar (which is very high in calories) and this is not specified. The point here is - they are talking about type 1 diabetes (requiring insulin injections) having a low fat diet. Whereas it is type 2 diabetes that needs to avoid sugar. Although a low calorie diet is also recommended to prevent the onset of type 1 diabetes and sugar is high in calories.
The Chinese hamster as a model for the study of diabetes mellitus. - PubMed - NCBI
Another University article (I haven't put the link as it may cause distress because it is about using hamsters for medical research), mentions that Syrians tend to be disease free, and if they do succumb to illness it tends to be respiratory, gastrointestinal or carcinogenic. There is no mention of diabetes in Syrian hamsters and it doesn't appear to be an issue, although it does say it causes dental caries in Syrian hamsters, so it would seem sensible not to give them too much sugary food also!
Vectis Hamstery's website has a nice concise version of most of this.
Diabetes in Hamsters - Vectis Hamstery and Exotics
So I can see that anyone with a dwarf hamster or Chinese hamster, will need to have a low sugar balanced diet, and it seems a low fat diet may also be helpful in Chinese hamsters according to the article above.
So regarding what the cause is and what the diet should be, (there was some disagreement on the other thread on diet) it seems both are right and it is a confusing issue, but it does seem common sense anyway to give hamsters a healthy diet low in fats and sugars, just as it common sense for humans, but particularly important for dwarf hamsters and chinese.
Personally I don't worry about sugars in vegetables as they are far lower than those in fruit and are natural sugars, but if anyone knows different, then please post!
The diabetic question
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