Do someone knows how the story system is handled in The Last Express?

In this game, the story follows its own route. It does not wait for the player. Every character has its own life. However, the main character/the player can still interact with the story. I don't know how to describe it correctly but things seem natural: https://www.jordanmechner.com/projects/the-last-express/

How do you think this system was implemented? Everything was made by hand? No AI system?

Thanks.