They didn't physically restrain him - not remotely. That's his drama llama ding dong outlook on it, but he's a bully and an unreliable narrator.
He chose to come back after they were all in bed, he was raging because nobody had gone running around after him, so instead of just leaving as he could have done at any point, he waited till they were in bed, made plenty of angry noise , berated her mother and ensured everyone knew he was still throwing his weight around.
At that point he got exactly the reaction he had hoped for, everyone was distressed and deeply upset. Her poor poor son was weeping and begging, as was the dog he likes to kick regularly, her mother. The OP tried to hug the vicious old bully and her husband briefly stood in front of him until the old bully threatened to hit him.
He was not physically restrained, at all, he was asked not to storm off by a deeply distressed family who were only deeply distressed because he wanted them to be.
And he's been continuing to torture his wife, daughter and grandchildren for three months since then despite receiving numerous grovelling apologies from them all.
The only thing any of them have done wrong is not to simply go non contact with with the old bully until he learns to behave himself.