Overground above Camden Market?

[Eibonvale]

Forgive me if this question only reveals my ignorance (!) but I caught this pic one sunday last month (the 18th - more details on my flickr photostream: http://www.flickr.com/photos/eibonvale/9536125819/in/photostream/)

This is the stretch of track that rides directly above Camden Market, London, linking the North London Line at Camden Road station with the lines out of Euston at Primrose Hill. What's puzzling me is that as far as I can tell this is not part of the Overground network, and yet several trains (I think with passengers) passed by as I watched. I am sure it is not earth-shattering, but I was just curious what was going on? Stock movement? Engineering diversion?

 

[bb21]

There were engineering works at Willesden Junction High Level and out west in the morning that day iirc, so until 12 o'clock, LO were diverted via Primrose Hill and the DC lines into Willesden Junction Low Level, terminating at the bay platform. Primrose Hill is not part of the day-to-day LO network.

 

[Eibonvale]

Thanks! That explains it.