ds2 was very like this. He used to sit on people he liked 
. He luckily had a twin sister and this mopped up the social side a bit,at home.
Ds was actually very lovely1:1 and very empathetic, and could play very nicely with one child at a time.
My view is that the school environment was quite overwhelming for him in many ways and this was the reason for his meltdowns, although he found it stimulating and fun too. He liked the rules and the organised playing but he found the free play the difficult bit. He found drama group or reading or talking (ie reading aloud) or answering questions a very enjoyable part of school, but he just could not cope with the social interaction when it was based on some unspoken rules that he had not mastered.
However, all is not lost. There are many options. Firstly I reduced ds's stress levels down by keeping him at a half day throughout most of Reception, he really struggled to cope for a full day. (People will tell you this is illegal and school should cope but I preferred that ds should enjoy school and be calm and happy to this principle) By Year 1 he was much better at sitting still and coping with less adult attention, the extra attention he got from being 1:1 massively benefitted him imho. He used to play very nicely byhimself when he got home on those half days, he was really no trouble at all, considering he was meant to be adhd/meltdowny. The environment made the difference to his stress levels/reactions.
Secondly, when things got much worse (he was by this point 9/10) he still enjoyed school,rules, activities,sport, but his ability to communicate socially was not being helped by being in school at all. He was singled out as odd and weird, pet of teachers but avoided by other children, social life collapsing, not invited to parties. When I made the life changing decision to home educate him, his social life became much much better, and he still has friends fromthat period, now that he is back in school. I can only think that again, the environment and the ability to tailor things to his needs, and to increase the chance of him successfully learning some 1:1 skills or 1:2 skills made the difference to his emotional state and his ability to cope with stressors/read the cues of other people.
Those who think children can only socialise if they go to school should think again, often home ed can be a chance to meet some much more INCLUSIVE families that put socialising at the heart of their child's educational experience.
To sum up, social communication skills are slowly developed, and with some children with ASD or ADHD they need a bit more nurturing, environments can help far more than therapies. Ds2 is 15 now, independent thriving extrovert lots of interests, drama gsce, hard working. I cried many tears when he was between age of 7 and 12 over social ostracism and his own failure to perceive how to communicate with his peers, but things are so much better now. For developmental reasons and because there was INPUT (and that input means, knowledgeable nurturing school, EHCP (we only got this at 14), and occasions for socialisation outside school)