The mother's description of what happened sounds coherent e.g.
“He’s been drinking and had me by the throat in the hallway,” she tells officers, adding: “I managed to get away from him but it’s like a light switch, one minute everything is OK and the next it’s really bad.”
And as far as the Judge is concerned, she believed there wasn't enough clear evidence:
“She struggles to give a clear and consistent account of what happened and when. I was also not able to get a clear account of how her injuries were sustained".
And the mother appears not to have cooperated with the process
“There was no statement made in the case, she is not here to give evidence, and she sent a letter to the court in support of the defendant.
“Given the issues with evidence in the case I cannot be safe in admitting it.”
So I wouldn't condemn the Judge who may have been obliged to come to that conclusion, and sometimes what is legally correct is infuriating, but that's not necessarily the Judge's fault.
The only good news is that 'himself' has had no contact with his mother since, and long may that last! She is obviously very unwell and hopefully she will get appropriate support and care now that people know what he's been putting her through.
That said, he's still her son, and the whole awful situation must be heart-breaking for her.