He wasn't left to go back to the hotel alone though?
He became unwell, his friends left him, he called his mum.
He then called a teacher.
He told his mum the teacher said she wasn't coming because she was "in a queue". That's all he said.
In the meantime mum had sent the teacher his location. Disney village, which, depending on where you are in the park can be a bit of a trek, particularly through school holiday crowds.
OP then later added that the teacher had told her they were trying to call his friends, and they were also going to him - for all we know they may have struggled to find him.
He was located, OP says, two hours later, and taken to sit in a cafe, with a teacher, until the coach came to take them all back to the accommodation.
A teacher DID go to him, and did then stay with him - the issue seems to be how long it took for them to get there.
DLP is large though, and crowded, and he was in the village which is a fair trek from the opposite end. It can also be quite difficult to find someone based on a location sent by a third party - what if he'd nipped into the loo to be ill and wasn't at the spot? They would have gone to look elsewhere.
The OP needs more information about what happened from the teachers before she complains.
FYI I'm a teacher too, with years of experience. It's taught me to get both sides of the story, not just parents/kids OR just staff, before making a judgement. The truth is usually somewhere in the middle.