Well, at first i thought amateur nutcase job, because the 'bomb' he made appears to be totally amateur and did not go off, it just smoked a bit they say. But with more news coming in it seems like it is some sort of Taliban retribution for actions done by the Americans in Pakistan. And to be honest i don't really blame them that much, killing people out of revenge is bad, sure, but so is killing someone in the first place just because you don't agree with them.
Oh, and the guy who spotted it and reported it to police was some t-shirt salesman, not the police themselves and the bomb itself was made out of "Police said the device consisted of propane tanks, fireworks, petrol containers, wires and two clocks."