According to some people it's not a habit, according to the book 'definition of stutterers' (over 600 pages) they explain that it's definitely a habit but only partial. In my opinion, I think that it's a habit but more in the sense of 'only looking for stressors' is a habit, the mouth repeating words is not a habit because it's only triggered by perceived stresses. By removing the habit 'looking for perceived stresses' in my opinion you reach fluency.