There are conflicting stories about where the exercises are. Your post states the "northern gulf", some research I did stated off the coast of Chab Bahar, which is in the south, well south of the Straight of Hormuz.
"Territorial waters" means nothing, as the ranges of a missile gone awry or some other accident could have happened.
My guess is this is not related to Iran's exercises, but you never know. After all, we accidentally shot down an Iranian airliner--remember that?
I have no idea if any of this is related or not. I even disclaimered FYI in my posting. It is significant to keep in mind though.