it is a mystery

Last summer my sister Lisa had an opportunity to have some watermelon with yellow flesh that a coworker brought to work.  She said it was the best watermelon she had ever tasted and she saved the seeds hoping to grow some this year.  I planted the seeds in the greenhouse this spring and when summer hit we planted the seedlings out in the "cornfield."  Unfortunately I planted them next to a watermelon variety that has red flesh and i have been hoping to be able to tell them apart.  So far all of my watermelons have been green and now I have this small yellow fruit where the yellow melons were planted. 

They are a little bit bigger than a lemon and have turned from green to bright yellow.  They are slightly soft, they yield slightly under pressure. 

It cut easily in half and there are lots of little tiny seeds and a softish flesh that smells kind of like a muskmelon and tastes just slightly more tart than a regular watermelon.  There is not a lot of usable flesh once the seeds are removed.  I wonder if the original yellow watermelon was one that was a hybrid and that the seeds grew a plant that resembles one of the parents from the cross.  Whatever they are i have a lot of them.  I wonder if they are something that should be eaten?