While there's all sorts wrong with this, he wasn't at work when this happened, he was in his own living room. The child wasn't anything to do with his work, it doesn't have to be for misconduct decisions in social work. I'm not sure why people are assuming that. The decision doesn't say who the child was or in what way he knew her. If she was related either to him or to his work I think would have been looked at differently. There's no way of knowing if she was "working class" or vulnerable in some way given it wasn't related his work. Misrepresenting what happens only makes it harder to discuss, though I imagine this being the internet calling out wrong info will be seen as thinking what happened was fine. It would be totally different if it happened while working.
However I do actually think it's a difficult one. Masturbating in a communal area of the (private) house with porn on is such a dumb, dumb thing to do. But he didn't instigate, encourage or let anything continue. Lots of creepy fuckers would. It's not comparable to having and maintaining a sexual relationship with a teenager. There's not continued dishonesty, grooming or intimidation. And a big part of the misconduct process is whether the worker shows insight and change around the misconduct which he has. I think there is probably a lot more information than is published as like a pp said they've really erred on the punitive side recently. I say that as someone who regularly reads the decisions. There's quite a lot redacted in this one.
When I was 15 I drank a beer and tried wine away on a naice French gite holiday with my boyfriends family. No one would paint that as me being given fed alcohol, it would be seen for what it was, trying it. I think lots of 15 year old have tried sips of alcoholic drinks. It's not the same as giving her a whole drink.