Sorry dude but this just isn't possible unless the trains were VERY poorly timed. The fact that he was in the front row is important. He would have already been going up through the loop or whatever is after that straight section by the time anything from the other train could have flown toward his (which is a distance of about 30 feet I'd estimate). It couldn't have been something somebody on the other train threw at him too. If it is something that came off a train, the most likely scenario is that it came from HIS train. And if it came from his train, the only possible scenario I can think of, again given that he was in the front row, is that he or someone else in the front row tried to throw something at the OTHER train, the wind resistance slowed it down, and he ended up getting hit by it in the face. Then again, if that did happen, it wouldn't have hit him hard enough to blind him unless it was a sharp object. Maybe he was throwing darts? Hmmm...
Long story short, it probably was just a big bug that happened to hit him in the worst way possible. Really nothing to worry about. Just a freak occurrence, although I will appreciate my sunglasses a bit more next time I ride.