Not always they arent. My friend had 3 mild strokes last year but luckly has never had another. She was only 37 but smoked and drank heavily. In my opinion she was a prime candidate to have further ones.
You are right to be worried though. The thought of being ill away from home is frightening. Are they intending to come home soon?
I hope all goes ok when he gets back. Then he can get to the bottom of it and get some medecation if necessary.