Yes you are right, he might truly not be able to say it. But from all the people who stutter that I have met (about 200), only one person, one time, was physically not able to say the word. The rest of us might take forever, stutter for 3 minutes, but we can still say what we want to say. It's just not fluent. It does not mean we can't speak at all. I was trying to give encouragement for that, but with your explanation I understand that in some situations it does not apply.