I know several Type 2 diabetics who are not (and have never been) obese. While obesity is definitely a cause for the disease, it is not the only cause there is.
I googled "diabetes in thin people" and found the term "skinny fat", slim but with a high percentage of body fat. These are people who may appear to their body to have enough fat stored to survive a tough winter. (This was how McDougall describes the onset of diabetes.) Can people with low body fat get diabetes?
Yep- it's in my family. Nothing to do with bodyfat. A body weight change of +/- 50 pounds makes no difference in fasting blood sugar. Hits later in life though (50s).