OP, it must all be a big worry for your family.
Having volunteered in schools, with y1, for years, I think it is fairly unusual for a school to exclude a child unless there was a serious problem with behaviour.
It seems to me highly unlikely he would have been excluded for accidentally touching/ hitting someone, as the school would have a field day with exclusions!
It sounds to me that the school is very bad at communicating with you, and very bad at dealing with behaviour issues in children.
Do you feel he has been excluded unfairly?
I have seen a boy who was constantly disuptive, agressive and a bit "wild" really, who was excluded only after a string of incidents, not a one- off thing. However, the mum was only told about the behaviour that led to the exclusion, not the whole hour of misdemeanors leading up to it.
So she was annoyed he was sent home for a little thing, when by the time she would come the teacher was often in tears and the whole class waiting outside so they would not get hit by flying chairs.
It is hard to really know what is going on. You need to talk to teachers, dinner ladies, anyone. What do other children say? What do his friends say? What is he like when he has a friend to play?
If the school, however, is really just excluding him for small issues and one- offs, they are overreacting and handling it badly.
They key is to find out what really goes on in his school day.