Hey Rock, I don't know enough about zuch shape genetics to answer your question.
If long is dominant to round then it could be a round parent in the hybrid.
A lot of magic happens in my garden,
things appear just by wishing for them or thinking of them, and then again,
things also appear when I don't wish or think of em either..... and I absolutely know, the secret to all that "magic" is the birds.
Heck I have found nutshells and peach pits in my garden that didn't come from my house at all, but likely were 'delivered' from someone else's compost.
with some birdly wishful thinking.
So if you have any flightful critters in the garden, or any squirrel etc the possibility that a seed was transferred from elsewhere cannot be entirely discounted.