The article does say that the teacher had been off previously for some time with stress. I wonder if perhaps he would have handled the situation differently if this had not been the case. Perhaps there was still something left over from that. Perhaps he could have grabbed the child harder than he thought.
It doesn't identify what particular needs this child has. Certainly his behaviour was challenging but that doesn't follow that he has a disability per se. If he had some learning difficulties then it would follow that he should be on some sort of plan and perhaps there was a need for additional support for him in the classroom. The child himself later refused to co-operate with the investigators according to the DM.
I don't think I do believe the teacher deserved to be sacked from the information given. However, I also don't believe that there is a full disclosure. I do suspect there may have been a failing in the school to the detriment of both teacher and pupil. It's very easy to get tied up with the naughty child or learning difficulties v the poor hapless/bullying teacher. Put simply, I don't think there is always enough provision for the child or staff. It is all very well having children with learning difficulties or challenging behaviours within a mainstream school and I certainly think it can be beneficial, however, the school must be able to support the child and staff or else it can a complete and utter nightmare for all concerned.