I’m thin and i’m a distance runner, and don't fit the demographic profile of a diabetic. Why did I get diabetes anyway?

Type 1 Diabetes. Type 1 diabetes, has nothing to do with lifestyle, it is in the mayority of cases an autoimmune disorder that you are design to get.
Probably type 1 DM. Most likely you have type 1 diabetes (previously called juvenile-onset or insulin-dependent diabetes mellitus). This is autoimmune condition --- immune system attacks and destroys pancreatic beta-cells that synthesize insulin. Special tests can diagnose type 1 versus type 2 dm (more common, usually in heavy sedentary adults). See an expert. Adult with t1 dm are different than children with t1 dm.