Other mistake: In the very first shot of Spencer, his coaches aren't textured.
Factual error: At the beginning of the episode, the narrator says that Connor and Caitlin are faster than Spencer, but Spencer, an LNER A4, holds the world speed record for steam locomotives.
Answer: Butch the breakdown truck must have pulled Gordon's tender all the way up the rails so the breakdown train can reach it and also Butch helped to get Gordon close to the winch.