Stolen bikes

My Brooks saddle and seatpost were stolen from Vestry Street, N1 between 2pm and 8pm yesterday:

The weird thing it, they actually left a different seatpost and saddle on the floor by my bike. So rather guiltily I tried it on my bike, found it fitted (though I didn't have an allen key to tighten it), and rode rather uncomfortably home. I did check the other bikes locked around mine and none were missing a saddle. Still I can take a photo and return the saddle if anyone can show a pic to prove it's theirs.

I can't work out whether the thief just nicked my saddle and replaced it for his own which he left on the ground. Or if he had stolen lots of saddles that day and for some reason - I refuse to accept considerateness - decided to leave one behind.

Why weird?
Most of the components probably gets nicked by other
cyclists, stealing for themselves.