The train is moving relative to the atmosphere held down by gravity where the volcano is not. Simple. Same reason you feel a lot of wind on your face if you stick your head out the window of said train. Get people that believe this shit to explain satellites, explain what you are seeing in lunar eclipse and what that curved shadow is during one that crawls across the moon. Get them to explain the classic of what part of a tall ship you see first coming in to port from the ocean and which part you see last using flat earth.
Or you could just believe satellites are made up, radio waves bouncing around globe are made up, what you see from high enough up in a plane is made up, pictures in space are made up. This HUGE conspiracy to trick people.