It was a lucid dream. Everything that occurred in the dream was a projection of my own mind. Every character, every vehicle, each dialogue, each expression given by the characters, every landscape, Everything.
I experiencing this lucid dream through the POV of the person on the left. We were talking with each other while the train passed besides us (which was also a projection of my own thoughts). The conversation was also a projection of my thoughts. As we were talking, I (the guy in left) said something (I forgot what I had said) to the guy besides me, to which I myself couldn't come up with a good reply. It was a moment of silence for a couple of seconds while we were walking. I was still thinking of a decent reply. But Out of Nowhere HE SPOKE.