Surely where there are two or more bidders it's bound to be a "bidding war". At least two of the bidders wanted the picture enough to take it to those heights.
The prices fetched at auction by Spare's pictures has been going up steadily for a number of years now. Recently we've had the Cuming exhibition, the BBC2 'Culture Show', and Phil Baker's biography, all in my opinion increasing the interest in Spare. It'll be interesting to see if this latest price is sustained over future auctions, or if it was a flash in the pan.