Sorry that is not a inflow. Here is a picture of what they look like and they seem to grow out of the top of the tip or down just a little bit. I have never seen one grow that far down. You plant look very healthy and with a little luck you will get your flowers next year. Hope that this will help. Barb

The tip is where you will see the first signs of an inflo. Next year you will have at least three chances to get blooms.

I'm not sure what that dark spot might be. It could be a left over undeveloped leaf that had not fallen off. A question in my mind is what did you seen when the plumeria branched three ways?