So one earlier part of the video around or just before ten minutes in he mentions how people say they are not like this everywhere but the tests they run still record how they are there. This is likely because anxiety/fear/pressure will compound the stutter effect. It all depends on how we feel about it. The words don't really matter. Like if we change our name, we'll still stutter on our name as it reminds us we COULD stutter on it, thus bringing up that vicious cycle of doubt and fear which tenses our stutter itself, like calling on it. So in a test environment, typically we and just humans in general likely worry more and feel anxiety towards being judged. So if they are in an environment where they feel people are more understanding and not here to judge you but to help you, etc, their guard is released more, their tension is set aside more and their stutter is not compounded so it gets them to feel closer to the way they feel at home. How many stutterers stutter alone in the shower for instance no matter what they say? It's a judgement free zone. So that's the simple truth of why results "differ" even with the same individual.