Respectfully, I would say you were wrong. I think the ideal way to approach a situation like this would be to talk to the individual privately about his/her performance. I can only imagine the fear within that person during the presentation, the shame and guilt afterwards, and then reading negative feedback that points out their #1 weakness that would just amplify the despair. When I give presentations in school (as a stutterer), I talk to my professors prior about my speech and ask them not to knock me points on things like eye contact and other pragmatics. Grading a severe stutterer on the performance of a speech is almost like grading a deaf person on a hearing screening performance. You have to make exceptions to people’s disability. Because for some, stuttering is indeed a disability. Thank you for your honesty in posting this. I know you mean well, but man, I really feel for that person.