I know that stuttering isn’t caused by confidence and anxiety issues, but therapy showed me (in my case) that my anxiety/confidence issues stemmed a lot from my stutter. I’m sure it’s not uncommon for people with stutters to have these types of issues too. They aren’t mutually exclusive. I enjoyed the show’s portrayal and even how he overcame a lot of his confidence/anxiety issues, but still has the stutter. It shows that it doesn’t magically go away if you gain more confidence and less anxiety.