When I think of it, it really seem as though he doesn't understand simple tasks because he is always expecting something more complicated. I will give him instructions and say this is all it is, he will follow up with " you mean I just..", "I just have to do..". Confirming over and over that what he is supposed to do is really just what I am explaining. It is like he is always suspecting there is more to it.
This is what used to be called "a lack of common sense." I think of it as an information-sifting problem-- this is a person who takes in a lot of information and thinks of many possibilities but has trouble choosing the most relevant or reasonable possibility.
It is also a perspective-taking issue (inability to think about the most likely meaning in someone else's head).
It is a serious hindrance. You can work on it by prompting him on how to think the task through. It's not an easy skill to teach.
He is also very insistent upon things being done right. One sheet of homework was counting fruits. The answer was supposed to be five, but one of the fruits was a cherry, not just one cherry but two stuck together like they are. But it is was still supposed to be counted as one. He refused to say they were only five fruits. He got very upset and kept saying there are actually 6.
This kind of rigidity is also important to work on. I would try not to cater to it-- we cultivate situations where rigid thinking is challenged. It is useful with worksheets to prompt thinking about "remember the main idea of today's lesson" and then "what do you think they are asking you to do here?"
Left unaddressed, this can become a problem with taking tests down the road, as well as a serious annoyance to co-workers.
This combination of features is often seen in people with autism spectrum disorders.
DeeDee