It is possible that their stutter used to be more severe. Personally, my stuttering was most severe in Middle School. My blocks would sometimes prevent me from speaking. A combination of age and good speech therapy has caused my stutter to become more mild. I still have stuttering moments but I have techniques (from my current speech therapist) that help me handle those moments in a way that makes me sound more fluent. I've generally become less anxious and more confident about my stutter, that also helps. You never know if someone understands you or not, how you meet someone isn't indicative of how they've always been.