a special needs 9 yr old child with adhd.
it makes me wonder if he was punished for seeking help because of not understanding.

adhd means he probably has difficulties focusing and difficulty being still.
I wonder what the teacher was doing to try to meet his needs.
it makes me wonder if the teacher was frustrated and ready to mete out punishment rather than education.
there are teachers who become so against a particular student they look for the first opportunity to 'make them pay'.

it's terrible this child was treated that way.
yes he probably needed isolation time. or to be redirected. a quiet corner in the classroom or proximity to the teacher would work for that.

if that doesn't work, other measures like a quiet space in the office in view of an adult.
calling the parent to escort the child during the school day.

but to deprive a child of bathroom privileges or other basic needs is cruel and abusive.