Have lower braces and a bone is protruding through gums, the dr says it's not from his treatment but that it happens when u move teeth. ?

Cannot say: without seeing it. My son had that PRIOR to the braces. Could certainly be possibly true.

Doesn't make sense: If you are stating that exposed alveolar bone is protruding through the epithelium, something is amiss. Bone should not be protruding. Even if the ortho treatment was not the cause , the treating dentist should have informed you about the condition before placing brackets and bands and moving teeth. Moving teeth do not cause bone to protrude through the gum... get this checked.

Second opinion: Bone should not be protruding out of your gums wether you have braces or not. In principle you can not get braces before taking care of broken teeth, treating cavities and getting a good cleaning. Any infection or abnormality such as protruding bone must be dealt with before placing the braces. Get your second opinion from a good specialist in orthodontics. Good luck.