That would be Ketones.
https://www.diabetes.co.uk/diabetes-and-ketones.html for some explanation.
Briefly, ketones are generated when your body burns fat for energy, so are usually in your blood every day.
People who are "in ketosis" or "keto adapted" are deliberately not eating carbohydrates but eating fats instead so that their body burns fat for energy, using ketones.
Ketones are only a worry if your body goes into "panic mode" because there is not enough insulin to get glucose out of the blood stream and into the cells so the body starts generating ketones instead. A mixture of very high ketones and very high blood glucose can be a very bad thing. Diabetic Ketoacidosis is a very dangerous condition.
This is
mainly a T1 thing but can also happen to T2s. It is sometimes the emergency which leads to a trip to A&E and diagnosis of diabetes. However many T2s are diagnosed long before this can happen.
I don't know, but I can guess that you were caught before that stage, but that your body had started generating ketones.
Ketones at low levels are perfectly normal, and a very good thing if you are losing weight because that shows that you are burning off fat.
If they fixed your high blood glucose at the hospital then any issue with ketones will also have disappeared.