Newly diagnosed child need advice on an incident that happened at school

Hi looking for some advice, my 5 year old child who has been diagnosed with autism. He is a lovely cuddly little boy who can at times get frustrated and lacks social skills to interact well with others in class, the school is very happy with his progress and haven't reported any issues at all.

i was approached by an angry parent on the school grounds who was accusing my child of pushing their child and said it was on a regular basis. I told them to speak to the teacher and stayed back to chat to the teacher myself. I was told that they weren't aware of anything happing at school and they had no concerns with my child.

a few days later the parent approached my child directly in the playground and told him not to push her child. i spoke to them directly this time and asked that they not speak directly to my child but to the school and that I had been advised that there is no issue with my child. To which the parent said they chose to believe what their child was telling them.

i am unsure how to deal with the situation as Im being told there isn't an issue by the school but this child is going home telling its Parents things that aren't really happening. The parent told me that MY childs behaviour isn't normal and this really has upset me - I am at a loss and sick of crying about this all the time. I dread going to the school incase another thing happens. Because my child has autism there is always a chance he can act out but he's adamant he's not doing what he's being accused of. 

Anyone had similar situations?