I'm sure that the person meant well and only wants to post the best content. However, this may lead to a negative environment for you if not addressed early. If it feels inappropriate, it most likely is, even if it was not said with malicious intent. I reckon maybe a bit more open-mindedness from your colleagues and they could do with doing some research on stuttering. They know you're in SLT, so obviously you're working hard on yourself and your speech. In my honest opinion, a genuine speech impediment is easy to distinguish from normal stammering that happens when talking or presenting.. and I wouldn't criticize anyone with a speech impediment who has the balls to get up and speak publicly. It's not easy to put yourself out there, I struggle with it, so the fact you do this as a job is seriously impressive. Keep going, trust your gut and stick up for yourself when needs be.