I haven't read the book yet so this is just my reasoning from what has emerged so far. I'm darned curious about the TRUTH and wish some award-hungry journalists were too.
I think you just about nailed it.
Pretty close, I think. Add that the Swifts fired at both banks to suppress possible enemy fire as Kerry accelerated down yon river. When it was clear that nobody was shooting back, it got quiet and Kerry apparently decided it would be a good time to go back and see how his "brothers" were getting along...