My bet is that though you couldn't see it (sometimes stray male flowers are in the buds), your plant self pollinated.
The fact you said you left it out 3 weeks longer reaffirms that this is probably the case, b/c plants that are keep out too long past peak harvest generally produce male flowers in a last ditch effort to pollinate the female. It's a survival technique by the marijuana plant to continue the plant's future generations.
Personally, I wouldn't dare start a seed from it, but people do it all the time. Just realize that your going to have to be extra careful in selection b/c they will have hermie tendencies.
Some will show early, some will show late and some will not show up until the future generations, but the herm gene will be more likely to come out b/c it was selfed.
Now, yes, even a male + female can have hermies, but the numbers are far greater in favor of having herms if a plant has been selfed naturally.
