Web design fail
It looks like their entire ordering system is indexed. Which, given that google only follows links, means that there's a link on their page to list all orders.
Also, the order numbers are sequential numbers, with no other validation like a login required... newbie web store error, meaning their entire system has been wide open for ages.
I really hope they didn't *pay* anyone to design that system, and the 12 year old they asked to do it gets a sharp talking to.