one of last scenes-I don't understand

Maybe I didn't watch the movie very carefully and that's why I don't get it, but please explain one thing to me. As we know from the beginning of the film,
Luc (Van Damme) and Andrew (Lundgren) shot each other. Now let's go to the end of movie when they fight again. Just before Luc kills Andrew by pushing him on the spikes, he recalls some non-existing event from his memory. In this short recollection, although it looks like scene from Vietnam, we see some other fight between Luc and Andrew. Luc kills Andrew, but not by shooting him as we saw at the beginning. When did this happen? Did he kill Andrew twice before the final fight? It doesn't seem too logical-after their death, they were turned into "universal soldiers", while in the scene I'm talking about it looks like they're still normal people, but I'm almost sure this second fight, remembered by Luc, never took place in the movie. I'm a bit confused, can you explain this?