As neither had a cough or fever when they went they didn't really break isolation rules even if they suspected it was coronavirus as back then the advice was specific to cough or fever.
As far as lock down rules go - according to the guidelines which he read out there was an exception specified relating to child safety. If he had actually broken a written rule he would've been sacked already. The reason they're arguing the case is because there is room for discretion where children are involved. That's why the media move the goal posts and argue about "the spirit" of the rules. Did he go against the spirit of the rules? I don't know. Maybe. But if I was in his shoes I would put my family above any rules - actual or spiritual. I wouldn't give my 4yr old child to neighbours or strangers. I'd give him to my family even if I had to travel. I'd just make sure I didn't come in to contact with anyone on my way so as not to put anyone else at risk.
I just find it hard to judge someone for doing something I would most likely do myself. Doesn't mean I'm saying that it's strictly right or wrong.