In light rail trading trains is known as a seat-swap. This happens when your train is so late that you are going outbound when you should be going inbound. Control (the dispatchers) tell you to get off your train and pick up the inbound train so where you get off where and when you should be.
When you are 30-minutes late on a 15-minute headway you are in somebody's space. A train shows up at the right time. It just isn't your train. That would be hard to do with one train each way per day.
At least Charlie Boyd got back to his home terminal.