I think the scales that measure fat only measure total overall body fat and are massively inaccurate, to measure visceral fat you need to have a scan. Not really possible but there is a body type called TOFI, thin on the outside fat inside (also toffee because you are shaped like a toffee rather than an apple or a pear) so even though you are tall and slim you could still be carrying a lot of visceral fat.
As for the diabetes diagnosis, you don’t give any figures (i.e. your HbA1c or even finger prick reading) do you know what they are. As for there being different types of diabetes, there are 3 types. Type 1, Type 2 and Gestational Diabetes. Type 1 you would probably have known about as it manifests from a young age or teens/twenties, Gestational Diabetes is developed during pregnancy so I doubt you have that, then there is Type 2 which you have been diagnosed as. If you numbers are quite low you could be pre-diabetic but without numbers I don’t know. When you see the nurse you might be given a glucose tolerance test at some time where you fast, then drink a sugary drink and have your BG tested at various intervals to see how quickly, or slowly, BG returns within a normal range. I personally had a HbA1c of 11.5 (very high) and my doctor just sent me for a second test with full instructions to fast although I had for the first as I was actually being checked for cholesterol but having a full blood works. My second test came back the same so I was put straight onto medication. Nearly 12 years ago diet could be tried but not at my level, it had to be brought down quickly, that was my downfall. Oh if only I knew what I know now.
Let’s assume that you do have diabetes (and I was slim when diagnosed 58kg but only 5 foot tall) and it is quite likely, although lets hope it is in the pre-diabetes range. Anyway saying that, here are 2 pieces of advice as you seem to want to know about it. 1. buy a book from The Dummies range called Diabetes for Dummies, it is excellent and simple and clear and easy to understand and goes through everything. Second, right now there is a course being run by http://www.FutureLearn.com called The Diabetes Epidemic. ust 2 weeks of a few minutes a day studying but you can take it at your own pace. It is free and open to anyone and should be useful to you.
If you have any more questions, I am not qualified but I used to be a registered nurse so know something, done the Diabetes course with FL and currently doing The Science of Nutrition with FL just because it interests me. So I dont usually talk out of my bum and if I don’t know the answer there are plenty on here who do.
Good luck.