There’s no way to know, since Mr. Mukasey is under no obligation to make his medical records public.
Several things can cause symptoms that superficially resemble a stroke, though. A simple bout of low blood pressure can cause confusion, slurred speech, and fainting.
I wonder if he locked his knees while making the speech. In high school marching band we were taught that locking your knees while standing at attention is a bad idea.