You are correct and yet what you are seeing is normal. The way it works is not black and white; it's not like you're telling the plant "hey you can forget about the main top and just make the side growths grow vertically"
The main top ofthe plant is still there! So what happens is, the plant still tries to grow vertically, with any top it can, and since the main top is still there it will continue to try and grow vertically. Which is great because the more the main head grows the more nodes appear and viola you've gt more side growths that can be potential new tops (if you tie down the head again)
It only appears as though The side growths aren't doing anything but trust that they will start to shoot up soon