Thomas and the Sounds of Sodor - S16-E11
Deliberate mistake: When the engines are performing "The Sounds of Sodor", Emily, Thomas, Percy and Gordon have the correct whistle sounds but at a lower pitch. At one point, James has Emily/Henry's whistle sound, Mavis has her old "New Series" horn, and Thomas has James' whistle sound.
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.