Hi!
Usually, children with autism interact poorly with others, are often unable to understand and control their behavior, thoughts etc. So, if he loves playing with others and even with strangers, autism is less likely. Maybe the child has attention deficit or is naughtier than others. There is no harm in consulting his pediatrician to evaluate his condition because this analysis cannot be done on net. If there is no problem identified, usually such children respond well to sports classes, hobby classes and if they engaged usefully. Hope this helps! Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.
I'm not a doctor, just a mom of a child with autism, but I disagree. Children with autism have difficulty in 3 main areas; communication, social and stereotypic behaviour. Your child clearly has delayed speech because he should be speaking at 5, he also has stereotypic behaviours such as lining up toys, head banging and rocking. The only area which is not clear is social, but social is not as clear cut as one would think. My son is incredibly affectionate, loves hugs and cuddles, enjoys playing with family. He loves to be thrown and tickled. He doesn't notice when a new person enters the room and will not say hello or goodbye but he likes playing with others. Also sometimes children with autism are overly affectionate and indiscriminately interested in people. Because your son enjoys strangers, it's more than possible he falls into this category.
He really needs an evaluation because to me (again just a mom who has been through autism and seen many a child with autism) he seems very likely to have it based on your description. Remember it's a spectrum disorder and no child with autism is alike. And also, given the severity of the symptoms (head banging and rocking and not speaking), I find it very difficult to believe he is being naughty and to treat this issue as though it is behavioural seems very wrong to me.