I didn't claim they were there, Iran did.
It was a ferry boat. It wasn't that far offshore.
Iran won't go more than halfway to Qatar, much less Bahrain.....that is where their "terroritorial waters" end.
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?