The thing is, the sleep questionnaire example is a different thing. That sounded like a quick screener designed to give a rough idea of whether somebody has unusual sleepiness or not.
The questionnaires you've done are longer and they are not screeners - I think you said there was 80 questions on one, or something? Those give a more in depth score, but they are different to screeners. You do not normally have screeners in an assessment unless they are screeners for other conditions, like ADHD or OCD or depression. A screener gives a rough answer - it tells you very quickly if the person should speak to a professional for a more in depth assessment. For screeners, it can help to do it with somebody who is trained to know what the question is trying to find out.
For long questionnaires they are not used as the only tool to answer the question of "Is this person autistic?" - they are not designed for this, and they do not give enough information. What they do tend to give is a score, in numbers, which can be useful to put in a final report and say "This person scored X in the Y questionnaire" because this can feel more "scientific" than a written description of what an interviewer noticed. And having both scores with numbers, and written descriptions means that the report in the end is more rounded and complete.
You should have at least one interview during your diagnosis - whether this was online, or in-person, and whether or not this involved any kind of tasks - like the one with a book with no words, or explaining how to brush teeth to an alien. The doctor looking at everything will use both the interview and the questionnaires.
With long questionnaires, each individual question is less important and it does not matter very much if you weren't sure what it was asking, because each question by itself the answer isn't important.
So what I mean is, whether or not you have trouble starting and stopping conversations is not what they want to know, even though it is the question they asked. It's the pattern across all of the questions. Autistic people will show one pattern, and neurotypical people a different pattern. You can see from this thread and other places online, that autistic people often find it hard to answer questionnaires because they like to be precise, whereas neurotypical people seem happier with answers which "sort of" fit. I think it might be that the pattern of different answers actually comes from this kind of confusion as well as autistic people generally having a harder time with social interaction, or whatever the questions are asking.