In the new movie Indiana Jones,How did Mutt (Shia Labouf) meet Indiana Jones in the movie?

Mutt caught up with Indiana just as Indiana was leaving town. He rode his motorcycle on the train platform, and basically yelled for "Professor Jones, Professor Jones", until Jones noticed him and, intrigued, got off the train. They go to a soda shoppe, Mutt shows him a letter from his mom, "Marion", and talks about Oxley. You probably saw them being accosted in the soda shop by the Russians, and their eventual escape.