First of all, lucky bamboo isn't bamboo at all, but a dracaena. I suspect that what you are seeing is where the new roots can form if you air layer or cut and root in water or a rooting medium. The roots will often form where there is a junction of a leaf and stem. Take a look here for more info on your lucky bamboo dracaena.
Here's a site on propagation.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.