Diabetes (as with much else) is a continuum. Many people are prediabetic, or experience periods of high or low blood sugar.

There are also multiple types of diabetes, not just the generally-known Type I / II split, but gestational (affecting pregnant women), Type 5, malnutrition-related, and others. (See Wikipedia for a listing: <https://en.wikipedia.org/wiki/Diabetes#Types>.)

Other factors can also influence blood sugars, including infections, physical activity, and stress.