oh, I don't know....sometimes they just get hyper!! I wouldn't worry about it, but if he repeats the behavior, and you don't like, you should discourage it by refusing to engage him in it. if he doesn't get any positive reinforcement from you, and finds you don't like it, he's less likely to repeat it.
yesterday Tommy jumped on my back as I was bending down to pet another cat, and my LOUD exclamation (his claws needed trimming), scared him and everybody else!! I think that gave him the message it wasn't appreciated. (I hope)