It's no joke when a train starts to smoke

Not comforting, but it was likely a grease box overheating.

The trains have a reservoir that is filled with grease (heavy stuff a little like Vaseline) at every wheel truck that will lubricate the bearings and reduce friction. If the grease box empties or it becomes blocked, the bearings will generate heat. Sometimes enough heat is generated to cause the grease to smoke, much like oil will smoke in a hot frying pan. They rarely ignite but will smoke quite a bit.

The only thing they can do is get it out of service and back to the shop and then put it in for service to clear any blockage and refill the grease system.