It shows the doc right with them, Zoey seemingly holding his hand even, on 123 when they are, what, at most 30-50 yards from the train . Then he just disappears for a few pages while everyone is getting on the train and trying to figure out how to start the thing, then he suddenly shows up again like he was way behind after they've started moving.
I can accept that maybe he couldn't quite keep up with them but what did he do? Everyone makes their last dash for the train and he says "You know what guys with the guns who have obviously been doing this for a bit, I'm kinda tired. You go on ahead, start that train up. I'm just gonna hang back for a second, no please, no guns for me, while this insurmountable hoard barrels towards me and you guys get the train going, then I'll catch up. See you in a few!"
If they wanted to have him that far behind they should have at least had him stumble on something and the others not notice he had until they get on the train.