“Too low” is a matter of context. If you have plenty of ketones to feed your brain, your glucose can go surprisingly low without ill effects. This was demonstrated by George Cahill in the 1960’s, in the course of his work on fasting in human beings. However, when the body is in glucose-burning mode and blood glucose drops, that is an emergency.
The key phrase is “that the doctors could find.” You may have been fine, or your insulin may already have been struggling to keep your glucose in check. But since the American Diabetes Association recommends not measuring fasting glucose, we usually never know there’s a problem until glucose starts getting out of control.