I can understand the blood clots being formed in the heart by atrial fibrillation (which sort of answers my question).
But it may be a translation thing... my belief is that a stroke occurs in the brain when a blood vessel bursts and causes bleeding and therefore pressure on the brain or a dying of brain cells because they aren't being nourished. It can be caused chiefly by high blood pressure. My mother had several strokes before dying from one. It is vastly different to a heart attack.