I wondered if he suffered the same type of stroke that my wife suffered last December. It was clot caused by a hole in her heart called a PFO (patent foramen ovale). The foramen ovale is a hole in the heart's septum that we are all born with, but in 25% of us, it doesn't close. The PFO causes agitation in the heart which can throw a clot in rare instances.
My wife was 46 at the time and in good health. her symptoms were partial paralysis in her face and arm as well as speech confusion. What caused it absolutely baffled the doctors. The PFO wasn't detected by ultrasound and was only found by an internal echo (down her esophagus). So she's lived with the PFO which went undetected for 46 years. She's since had a device implanted to close the hole.
It was freaking scary. Eight hours after the stroke, she couldn't sign her admittance form. 10 days later she was back at work as a professor with no lasting effects. She only told a few coworkers what actually happened and most have no idea that she had a stroke.