Not real sure what makes a few of them grow multiple tops.
I have found several with 2 tops over the years and one with 3 (3 prong) tops that was a really nice root.
I'm not sure about the 2 seeds in one berry somehow merging together. Think I would lean more towards some type of damage to the root neck causing that, or could just be that the plant was growing in ideal (root) conditions and the root could support multiple tops so it just sent up another.
May never know the answer to that one for sure.
Here is a pic of the 132 year old root from Scotts book.
Looks like it had 2 tops.
You can see one curl going up off the main root and another curl leaving it and going over to another root. Strange.
TNhunter