Factual error: In the Bosphorus scenes, as the ferry crosses from the Asian to the European side of Istanbul, in the distance large trucks can be seen speeding along the coastal road opposite. Well before their time.
Factual error: The same locomotive is used for the entire run of the train, from Istanbul to northern Yugoslavia. This is impossible - locomotives would have been changed at the Greek, Bulgarian, and Yugoslav borders, at Belgrade, and perhaps at Nice.
Factual error: The Locomotive pushing the snowplow close to the end of the movie is a French 141 R. They entered service from 1945 on, ten years after the movie is set.
Factual error: In Istanbul we hear the standard Arabic-language call to prayer (beginning "Allahu Akbar!"), but the film is set during the 1930s when Kemal Atatürk was in power and muezzins were required to use a Turkish-language call to prayer (beginning "Tanrı Uludur!") instead.
Chosen answer: They planted this red herring not to divert Poirot's attention away from them - they were the only passengers on the train - they wanted to divert him from the fact that they were ALL involved in the murder, because they all had a common bond with the child whom the victim murdered. Each one made out like they didn't really know anyone else on the train, but they were all in on it.
Kimberly Klaus