It seems many people with intellectual disabilities can be more socially immature or inept than many (high-functioning) autistic people. Some autistics refer to people without autism but with an intellectual disability as neurotypical but I don't feel they are.
Today I met my partner's friend's daughter, a 24-year-old with a lifelong intellectual disability caused by Fecal Alcohol Syndrome, but isn't autistic. She lives with her dad, who looks after her because she is unable to function alone.
She showed me her phone and excitedly said that she has loads of friends on it, then showed me her contact list, which only had 4 people she considered friends; her dad, the lady who ran the MENCAP group, her social worker, and a girl with Downs syndrome who also attended the MENCAP group. But to her that was "loads of friends" and she was very proud.
She also has a strong attachment to toys and takes one of her dolls out with her. And she apparently really fancies this young man who lives next door and is the same age, and told me she wants to go out with him but doesn't know how to talk to him - even though he apparently is friendly to her but otherwise isn't interested, as he already has a girlfriend (I assume him and his girlfriend are neurotypicals).
So, yeah, people with intellectual disabilities struggle too and can be clueless of social norms, naive even. Also she doesn't like balloons because, as she said, "they make a loud noise". So she told me (in her little childlike voice) that she'll invite me to her next birthday party but that I mustn't bring any balloons. I promised I won't.
I actually felt neurotypical compared to her, me sitting with my partner chatting about normal adult subjects with her dad, such as work and money and shopping.
I did find the girl sweet though, and I will come to her birthday party, even though she wants to play 'musical chairs' and other childhood party games. But if me coming too will make her happy then that's nice.
Before anyone says "oh but the difference between intellectual disability and autism is that people with intellectual disabilities are still social", that isn't strictly true because it's implying that autistic people typically aren't social. I'm sociable for an Aspie, while I can be shy I still have a socially functioning mind that naturally makes me desire to be accepted and have friends, just as much (if not more) than this girl with a learning disability. In fact I seem to function more in the neurotypical world than she does.
; which is what not-autism is whether or not a person is neurotypical or neurodivergent.
All neurotypicals are allistic, but not all allistics are neurotypical.
Your partner's friend's daughter is an allistic neurodivergent. One is not merely a neurotypical for merely not being autistic.