Well with you saying that he was lethargic and off his food, and thinking that maybe he has pancreatitis, if he is not getting enough insulin, then it can lead to the perfect storm, that leads to development of ketones.
Some cats seem to be more prone to it than others, George has certainly been sick had numbers in the black, not eating etc and never developed ketones. But it is a concern, hence asking about getting that ketone test.
The fact he is eating better today, behaving more normally and his numbers came down, is a relief.