Car Sideview Mirror Explosion

It’s possible something actually did hit the mirror and you didn’t see it. Years ago I used to ride a motor-cross bike(dirt track motorcycle) During one ride at about 50 mph my plastic helmet exploded for no apparent reason, split in half, fell off my head and onto the road. I had no idea what happened, but the rider behind me said he saw a low flying pheasant (large game bird) hit it.