That's the standard advice, but fasting is incredibly good for type 2. Edit: that's a good way to manage type 1.
Dr Jason Fung's The Diabetes Code is a very good book on the subject.
Type 2 diabetes is all about insulin resistance. Insulin transports glucose into cells. The cells use said glucose to perform tasks. Insulin resistance happens when the cells are already super full of glucose. Why are they already full? Because of eating too much sugar, too often. Over time this resistance gets to the point where glucose in the blood is too high for insulin created by the body to push into cells; at that point we call it diabetes.
You can always brute force more glucose into cells given enough insulin. The body, in fact, ramps up production of insulin higher and higher to force more and more sugar into the cells. It's the excess sugar in cells that damages the tissue of whatever organ. A typical insulin prescription is sliding scale based on blood sugar before each meal. Typically no more than 10 units. Standard prescription is 4 pens for a month. Many diabetics go through half a pen or vial a day. (How they afford that is a mystery I hope I never have to answer)
Fung says (and my own observations back him up) that fasting AND a low-carb diet decreases blood sugar overall by allowing the tired, overworked cells to burn through more stored glucose. With regular enough fasting this lowers insulin resistance. With lower insulin resistance you can reduce the amount of meds taken. With super strict consistency it's possible to get off all drugs, although that's unlikely to be the primary way to manage diabetes for most people because it requires a 100% commitment for life. Because even if your diabetes is in remission you're still diabetic.
The number one rule of fasting, diabetic or not, is go by how you physically feel. Coco could go for two or three days without eating more than a couple hundred calories, if anything at all, because her insulin resistance is so high, without feeling the low blood sugar jitters. But if at any point while fasting you find yourself getting hangry or the jitters: eat something. Something low in carbs, of course. Most fasters do two meals a day, but one meal a day is fine too. Some fasters do 24 hours a couple times a week, eat normally (but low-carb) the rest of the time.
Coco will do none of this, because muh eating disorder. Hell, I clearly know all this, have irl data that backs it up and still struggle with it. It's fucking hard. But so many diabetics won't even try. Not even after losing limbs.
Edit: the standard advice is mostly because the majority of type 2 diabetics won't adhere at all to any diet that makes them slightly uncomfortable.