My sister is ADHD so she legit has real questions that I can totally help with despite having seen the same stuff so far. But of course she has no idea which stuff is intentionally vague and which stuff she hasn’t been able to connect that was intended to be solved so far. So if it’s an intentionally vague moment my answer is “we don’t know yet”.
I definitely get that it can be annoying if you have no idea why they are asking. But they wouldn’t have learned that behaviour if it didn’t occasionally matter. Since this behaviour is common, and ADHD is common, I wouldn’t be surprised if it’s always the case. But it’s probably only some people with ADHD, depending on how theirs presented. And of course some people may have this trait of ADHD without enough of the rest of the traits to be able to get diagnosed.
But yeah, it’s one of the traits of ADHD that makes them feel like they must not be smart, despite any evidence to the contrary. Cuz they just don’t “get” what are obvious clues to other people. But it’s simple topic linking, basically their brains see everything in it’s own bubble, and they can be very good at figuring out everything in that one bubble, but if a puzzle in that bubble needs a part from a different bubble, that puzzle is never gonna be solved for them without outside help to find the bubble that has the needed part.