What was the explanation of the 51 people burned alive on the train in For Greater Glory?

In For Greater Glory: The True Story of Cristiada (2012), there is a scene in the first half of the movie in which a train is robbed by the Cristeros. Padre Vega, who is in command in the scene, asks one of his subordinates if all the people are off the train, to which his subordinate answers "Yes." They then light the train on fire, and screaming is heard from the back of the train. Padre Vega shows a concerned look on his face.

Through the rest of the movie, Padre Vega takes a lot of flack for having burned "51 innocent people" alive, and Vega half-heartedly defends his actions as revenge against the brutal Mexican government.

What is the explanation of this plot element?

• Were the people burned unintentionally?


• And if so, did Vega intentionally kill those people, or did his subordinates subvert his authority to kill them?


• Why didn't they try to rescue the people from the train when they were found to be still aboard?


• Why did Vega explain his actions, rather than saying it was an accident?


• Who was actually killed? Civilians, or Mexican federal soldiers, or someone else?

As this is based on a true story, if it is better for me to ask this question on History.SE, I can do that.