Autism and intellectual disability (formerly called mental retardation) are two different things.
People with autism generally have no issues with intelligence, but do have issues with social interaction to varying degrees (which is why it's now called 'being on the Autism Spectrum'). Unless they're on the severe part of the Spectrum, they can live and function independently, although they may need support for the problems with social interaction. Many of them are isolated.
People with intellectual disabilities have less intelligence, usually need some supervision throughout their lives (although some can live independently with less frequent supervision), and frequently have chromosomal abnormalities.
In a nutshell, that's the difference between both conditions.
Now, we all know people who are a bit "slow", but may not be to the point of being intellectually disabled clinically. We also know people who are "socially awkward"; many of these people are somewhere on the Spectrum and/or have some other mental health issues. There is a lot more detail to these issues than I can describe here.
It would be interesting to see some posts showing Black people with either of these conditions.