NTs would use it as a euphemism ... as in "He wasn't exactly a genius, if you know what i mean!" They'd end this sentence with a slight head nod and a simultaneous half wink to make sure others would know they really meant "He was stupid!" This is so as not to appear "rude" by describing someone as stupid. Even if this is true, it is considered a bad thing to do in NT circles. Even though every NT within earshot knows that this is exactly what is happening, they all feel better about themselves whilst doing it.
It's their weasel words, saying one thing but meaning another, goes on all the bloody time and i'm only now at 44 getting to see it, or at least the more blatant ones.
So when talking about themselves they couldn't say "I know I have a low IQ." Because it would make them feel bad. So they swap it around to make it easier to face by saying "I know I ain't exactly a genius Doc!" The doctor would then know the patient was admitting to being of low intelligence... if this was two NTs talking the code works a treat. The patient only admits to being "not a genius" (after all, genii are rare and strange people right?) and saves face in front of a higher social ranking figure of authority (the doctor) and both parties save social embarrassment.
But, if one party is an aspie... then it all goes tits up. The aspie doc thinks the NT patient is stating the bleeding obvious and wonders why he bothered! "You're right Mr. Typical, you are not a genius."
But if the doc is NT and the patient an aspie, as in this case, then the data gets so corrupted by NT stupid social rules and traditional euphemistic behaviour that the meaning is totally reversed. The patient says "I realise i am not a genius." A statement of fact, some of us are lucky enough to have savant streaks within us, some don't. Many NTs expect us all to be able to copy a Picasso at one glance with only a twig and two shades of mud to do it with! But as we know this, sometimes they need telling that we're not all bloody genii and most of us are normal and upwards.
But the doc hears the age old euphemism ""I know I ain't exactly a genius Doc!" and automatically, without thinking (which they do a lot!) writes down "Patient realises he is of low IQ." or some such. Thereby missing the point of the statement completely!
And they wonder why they exasperate us so much! It's taken me till middle age to put together enough of their damn stupid behaviour to flesh out what's going on in a situation like this, and quite a lengthy post to jot it all down. They do this automatically, yet it is all largely unnecessary fluff. Convoluted rules and ritual over complicating things when a simple statement and a literal reading would have done in the first place!
Try explaining a simple interaction like this too them though, step by step, and they'll say we're looking at it too deeply or reading stuff into it that doesn't exist. But it seems to me this is what went on here... all in a few seconds and we're left gasping going "WTF! What just happened there?" And having to work it out step by step later on.