You’re right that it’s more commonly seen with an autism diagnosis, but it can be true of those with ADHD as well. Many are literal, concrete, black-and-white thinkers. They have to learn to look for and interpret body language, tone of voice, and other nuances to see the actual intention. My son has both diagnoses and really struggled with concrete thinking, especially with analogies and figures of speech, for many years. Around middle school he started to learn to pay attention to unspoken language/communication and does a LOT better with it now, at 17.
My son’s autism is very subtle and took 3 clinicians to diagnose because he kept getting dismissed for not having the stereotypical autism symptoms. Personally, I believe ADHD and autism are one spectrum together.
All that to say, your son could very well struggle with this and have just ADHD, or he could have very subtle autism along with ADHD. The answer will differ based on the clinician you ask, unfortunately. The bottom line really is to work on building his non-verbal language awareness and skills.
ADDitude Community Moderator, Parenting ADHD Coach, Podcaster & Author, Mom to teen w/ ADHD, LDs, and autism