This is the first time I have noticed the mention of supressive fire from the other boats"
Page 90 " Unfit For Command "
"The boats had begun firing after the mine exploded, but they ceased after a short time because of the lack of hostile fire."
Kerry was long gone by then.
If Kerry's boat went down the river a ways after the mine blew up the other boat, it would be easy to mistake the supressive fire for hostile fire, if you were a ways away. Also, Rassman said, on TV at one point, that he was diving to the bottom of the river to avoid the propellors of the boat and what he may have thought was ememy fire. It must have been disorienting to fall from the boat and that could cloud his perception.