Yeah I agree Dave, It's a combination of both, but I would say technique is more important. Good technique alone will get you sidehopping very high and then when you get towards a limit "explosive strength training" would probably improve you that little bit more at the top end. Look at Gilles Coustellier for example, he is not bulky or over built at all, but he has so much technique that it doesn't matter. Also you could look at TRA and Benito Ross like Dave said, they are pretty well built and can sidehop houses.