What do you think about this case - child abuse or no?

child abuse.

At the start of the report it did not seem like child abuse as he was not locked in nor handcuffed, so he did have the option of going out of the room, moving etc.

However, when the mother begins handcuffing the boy to the chair, then it becomes child abuse.

No. The use of handcuffs might seem excessive to some people, but he was never in any danger and having them on didn't harm him physically. He could move around as much as he could if he had broken a leg and was wearing a cast, no more confined by the cast than the handcuffs. So he was somewhat more restricted than if he had simply been locked in his room, but not much. His complaints are IMO unfounded, and I come from a childhood where severe abuse was inflicted upon my siblings and I constantly by our mother, so I speak from personal experience.

Also, it might be noted that the boy asperated the situation he was original in which brought about his mother then using the handcuffs to restrict him more effectively.

ABSOLUTELY. This parent needs to be thrown in JAIL.