methinks you are reading way too much into this. It is clear from the problem that he built only as many as he sold. Think of the good professor building widgets only on consignment, so when he gets his order (prepaid in full of course) he then makes it.
Your assumption is ok for big business i guess, even though they do not make as many as they can, they make what they think they can sell, and allow for some overstock usally. which is a far cry from as many as they can.