Ahh..I see the lil node in your whole plant pic.
Its just a shoot that went its own way. I had this with one of my autos
Its just a mutation.
Foxtailing it's not.
You can either leave it r pull it. Me id leave it.. plant mutations can be interesting to see develop. You might get a few inches of a nice mini cola.
Good Luck
High Elpicor, you did not do anything wrong and the plant is looking amazing! It is just a mutation like you thought already. Enjoy the rest of your grow and the harvest!