LOL, some people seriously can't comprehend you can still get good a good amount of conversions even if your daily unique visitors is around the 300 mark? There's a reason why you should strive to rank for buying keywords and not info keywords if you're trying to push a product/affiliate products.
No doubt he's also ranking for other terms as well.
Nothing to hard to believe here, well done OP! Just try and figure out what you did to get to the top, then rinse and repeat!