High blood sugar should be considered a symptom. High blood sugar can be caused by:

1) Having enough basal or "baseline" insulin but eating too many carbohydrates. This will lead to a high blood sugar reading but no immediate danger (this will cause long term health issues like kidney failure, blindness, etc if you run a high average blood sugar over time.)

2) Not having enough insulin which is incredibly dangerous. This will often presents with high blood sugar but not always. Your cells are not getting enough glucose. Your body responds by releasing lots of short term energy stores. The stores that become glucose still can't enter your cells since there is not enough insulin so your blood sugar will often read high. Your body also breaks fat into ketones which use a different mechanism to enter the cells and don't require insulin. Ketones can provide the energy your body needs and keep you alive for the short term, but they are acidic and will kill if the concentration gets too high (diabetic ketoacidosis -- your blood pH changes enough that it interferes with the normal chemical reactions your body requires)

So the real test for dangerous situations when experiencing high blood sugars is to test your urine for ketones.

From the FDA article, it sounds like the CGMs were incorrectly reporting low blood glucose values for extended periods of time. The closed loop pumps respond to a low blood glucose by lowering the basal rate of insulin. The is dangerous if done for too long a time. Also note that insulin response varies wildly by individual.

From the pumps I use, there is a maximum basal rate adjustment allowed before the pump alarms and kicks you out of the "insulin auto-adjust mode". This was with both medtronic and tandem pumps.

I haven't used the abbot cgm or pump. I would expect there would also be limits to how much the pump will lower your basal insulin rates before alarming. I haven't seen any specifics, but I bet the software bug is allowing a lowered basal rate for too long under continued false low glucose readings and patients going into DKA. (IMHO bad sensors should be accounted for in software and user alerted under any suspicious circumstances)

Needless to say, this is a horrible situation and my heart goes out to everyone impacted.