I'm still trying to work out how they managed it. I suspect they removed their key from a door panel without thinking, to investigate a problem on the platform - but because they had already closed the other doors, removing the key triggered the local door to close behind them leaving them stuck on the platform.
At least it's not a long run for the PSA from West India Quay to Westferry ;D
I always thought that simply removing the key won't allow the train to drive itself. I thought a button has to be pressed next to the PSAs door for the train to move. Unless of course the button had already been pressed, and the key removed, but the PSA's door hadn't closed?
It wouldn't surprise me if wasn't the first time this had happened on the DLR.