Type 2 can also be inherited and/or age onset. Being overweight however, does play a big role when it comes to type 2 diabetes as your pancreas is effected by the excess fat in your body (specially round the middle) and so doesn't produce enough insolin and when you lose weight, in many cases the insolin production goes on as normal, medication is no longer nesessary, but diet IS..... but no, not all type 2 diabetics are overweight.
I HATE when people act as if all overweight people are lazy slobs who sit around on their behinds and eat all day long. That is in some cases so, but not all do that. In my case I have had an undiagnosed underactive thyroid gland for years, which lead me to gain a lot of weight and my father has age onset type 2 diabetes (he's not overweight) so I could have it because my father has it or because I am overweight... In any case, I don't care why I am diabetic, I just am!!! I now take more care of myself and lose weight with help of my thyroid medication, exercise and diet....
And by the way, my aunty (father's sister) has been overweight all of her life, is in her 60's and doesn't have diabetes at all.... Hmmmmmm Not all overweight people do get diabetes either....