Left North Greenwich... at 4:45am?!

The system is very good at watching what are normally trains during the day. However, during the night various track circuits may drop and show "occupied" for a number of reasons connected with maintenance. As they are not trains that have been signalled in the conventional sense, the system is not passed a train description, therefore all you see is the "default" description of "special" or "not in service."

However, it could also have been an engineers train. We have those too. It's a myth that after the last train the system closes. To customers yes, but to staff it never sleeps.

As for this system displaying train descriptions, this is taken from the signalling computers and not from the front of the trains themselves.

It's all very clever, but was designed for those people looking in during daylight hours ;D