People with autism do not pick up social cues like other children. They have to 1. Be taught these things actually exist, 2) To consciously look for them (this often results in awkward looks from the people they're monitoring) and 3. Practice them. They might one day begin to come naturally but not always. Sometimes an autistic person must always be conscious that they have to use non verbal body language and read it in other people.

Missing out on social cues because of being overwhelmed by the environment because of a different processing system is more an ADHD thing. Then again you can have someone with both autism and ADHD. Maybe the processing is similar in both conditions but you can put an autistic in a calm environment like the family home and they still wouldn't be able to pick up on social cues.