Kids teasing my son as Autistic

This happened in Singapore in a public playground just right below our HDB. I am a mom of a very loving, smart and kind 5 year old boy. We are from the Philippines and due to circumstances not disclosed by SG government, we are unable to obtain a student pass for him until after four tries. We try our best to home school him although social skills need more improvement as he can only interact with kids when he goes to the playground. There was an incident where he was trying to approach older kids in the playground but they kept shutting him off. I am not sure what is the reason but I tried to observe the best I could. My son is talkative and won’t shy approaching other kids first. I can see from his body language that he wanted to be included in games and make friends. There was this instance when I heard him saying to the older kids that the “playground is a truck” maybe playing pretend/ imaginative play. My son speaks fluet English and his accent may largely differ from SG English as he watches a lot of American shows. I was thinking that maybe they couldn’t understand him. However, the older kids suddenly told him that he is autistic. After a few seconds, they were chanting. I did not know how to respond, although my son thought no harm was done to him, I asked him to leave the playground. I know that my son is not autistic as I am a Psychology graduate and we evaluate these things from the onset. However, I was very upset that other kids would think of him like this and exclude him. How do you cope with this kind of treatment and how do you explain such situation to your child? #firsttimemom #playgroundinsg