I just don't understand this at all. I have read so many incidents like this. I worked in education for over 20 years, almost all in Special Education. I have never had a situation that merited holding down a child, and tying him up.
I am sure that these teachers have had training in restraining students, that uses physical restraint. More like giving a child a big bear hug. Never ever using any type of ropes to tie kids up. And if you do any sort of physical restraint, you have to fill out a load of paperwork.