He hasn't stopped stuttering. It's always there. He says at the end if he drinks and there's a lot going on he stutters. During this segment you can hear him on the verge of stuttering several times but he doesn't allow it to happen. It sounds like he has a very mild stutter and that his inner stuff exasperated it. The shrooms/stepping outide of himself and positive experiences like talking to that girl reframed things and he developed the confidence to speak.