I'm wondering if the memory that was seared into Kerry's mind wasn't a hallucination from seeing Apocalypse Now 5000 times.
Apparently Kerry has mistaken himself for the character in the movie. That's pretty S'kerry.
I recall that, as the boat was going up river into Cambodia, there were lights strung across one of the bridges, fireworks going off, and drunk or drugged-up soldiers firing wildly. It could have been Christmas. However, I haven't seen Apocalypse Now for many years.