think about it for a minute.

if all seeds are meant to be female, then how does the species survive in nature? You need boys ya know..

your friend probably bought feminized seeds which are developed in a special way so that they all produce female or (occasionally)hermaphrodite plants. Feminized seeds do not exist in nature, and are a result of mans intervention, and are not the same as normal seeds you buy from most banks, they are a very specific product.