The only way to get seeds is from the pollen of a male plant. Your friend probably had a hermaphrodite in the grow. Or he didn't notice a male until it was too late.

All strains of cannabis are designed for making seeds. If you pollenate them they will form seeds. Cannabis produces a LOT of seeds when allowed to propogate.

Hermies can hide the male flowers very well and it's more then likely he didn't see a few male flowers.

Was he using feminized white widows?

Laterz