There's also a pretty solid possibility that these people were celebrating the end of the war - not the bombings, necessarily. I know I'd be pretty excited if a long, bloody war just ended. I'm pretty sure these people were thinking "Thank God I don't have to go fight and die in the war now!" rather than "smurf yeah! We just killed a load of dirty japs! Yee-haw!"

Also, the pictures were taken on VJ-Day, which was several days after the bombings. If these people were celebrating on the day we dropped the bomb, you might have a point.