I think it was on the market for a bit over £400k so they bought it for under. Can't remember exactly.
It's a crazy selling price though. It's an odd part of Kennington, a bit of a no man's land between Kennington and Elephant and Castle and in the middle of of a bland new development.
Nothing round here sells for that kind of price. The next most expensive house on the market seems to be this
http://www.zoopla.co.uk/for-sale/details/26563170?search_identifier=596b88b0f01dae97f0c9b205434afa1d
Which although a very different types of property has loads more land and is in a much better location. It's been on the market for ages too.