I doubt anyone that was sounding like Joe Cool, would be suffering from hypoglycaemia. Their bold, erm, and spelling.
These are often called the “warning signs” of hypoglycemia. Lack of glucose to the brain can cause trouble concentrating, changes in vision, slurred speech, lack of coordination, headaches, dizziness, and drowsiness. Hypoglycemia can also cause changes in emotions and mood.
I've told so many tales of bewildering things happening that you might think I'm not fazed by this accident. But I am. Bewildered. I can usually come up with some bit of lateral thinking that would explain things, at least is someone's universe, but not for this. Given their speech wasn't slurred (ATC data) then there's not much left but a native incompetence that has been rescued time and again with automation. But I somehow I even doubt that.