Most strange. Please could you check from 0900 to 0930 - he is quite a late arriving person coming in from darkest Essex. It was definitely a Circle Line service he picked up at Liverpool Street. Commuters being creatures of great habit, they all ended up looking very confused at Baker Street - he said - having ended up at a platform most had never seen before. Might as well have been Platform 9 3/4 !
Thought, before GoldenArrow's post, that someone had taken 'a wrong un'.
Just a thought, would the controller have had to renumber the Circle Line service before the system would send it up the Met to reverse in p2?
I've checked Trackernet Replayer from 09:00 to 09:45 but still can't see a train with a 200 or 170 number going to platform 2. Ask your mate roughly when he got on, I'll follow the trains to see if maybe one was renumbered.