That's not entirely true. Weight and diet are definitely risk factors, but so are age, genetics and a history of gestational diabetes. The main thing is that your body becomes resistant to insulin for one reason or another, causing hyperglycemia. Whereas with type 1 your body stops making insulin entirely because your immune system destroys the insulin-producing cells in your pancreas, to the same result.

It's a common sentiment that those who have type 2 are to blame for it, but I had a professor at university who was rail thin and active and had type 2.