Depending on where you live, it could have been open pollinated by males in Grandpa's or someone else's grow or - in the american midwest - by industrial hemp or "ditchweed" - wild hemp left over from industrial grows before prohibition.
Is it okay to smoke? You said it was grown on the "open farm." Was it close enough to other crops to get sprayed with pesticides or other agricultural chemicals? If so, would you want to risk it? Otherwise, sure. But you can do a whole lot better. Haha, you should point Grandpa to this forum, I'll bet he could do a lot better.
Welcome to RIU. Read, read, read and grow some dank weed!