I don't think you know how social work 'works'
A social work manager only knows what a social worker does by what that worker tells them. And in terms of the 'whole department' I don't have a clue what my colleagues are doing - if I check their diary I might know they're at a core group or 'on a visit' but I wouldn't know what they're doing when they're out there unless they specifically told me, e.g if they needed help.
As a manager you supervise, but given you might have 2 hours a month to supervise and discuss 30 children along with everything else you do in supervision, you rarely get much detail. It's entirely possible that the social worker could have minimised what they shared with the manager, and the manager would be non the wiser. That's why integrity in so important in social work because you have to willing to tell your manager if you're unsure, or struggling, or unsure of your decision making.
In terms of the 'climate' no one recognised grooming the way we do now, twenty years ago. And teenagers were definitely seen as older and more responsible for their own decisions (when you think about it, 16yr olds used to be able to leave school and work full time and move out, that seems ridiculously young now)