I believe him. As soon someone who has stopped stuttering myself he does point out that he has to trick the brain to get out the rhythm planning of repeating words .. In a stutterer mind the stutter tends to focus on the word so much that he/she doesn’t realize they can say/ think anything else besides that word and just speak.. with his spiritual awaking with mushrooms my guess is that he was tripping so much that his subconscious was so open for suggestions and that reinforced his belief/determination to stop stuttering.