I agree with the above comment. I’d also remember that anything the nursery does is a collaboration with parents. You can and should express your thoughts throughout the whole process. Suggesting some quiet time may be beneficial in assisting the staff into implementing the right support for him. I’d also argue that what your son is doing is developmentally normal, and I presume the nursery staff recognise that too. They just need to balance your child’s needs and development with the safety of other children.
Hope you’re getting on okay x
Id imagine that it’s overstimulation like you say. I think it’s great that they’re wanting to do ABC. Hopefully that means that they’ll come to the conclusion themselves that he would benefit from some quiet time each day and it will ultimately help him. If they’ve said they’re not concerned then hopefully they aren’t punishing him for it either and just trying to get to the route cause