It's one of those rare occasions when he's actually making a good point - there's almost always a 'How did this man get away with abusing so many children for so long?', 'But he was such a respected Pillar of Society, it's inconceivable that somebody like him would ever do such an awful thing, surely it's a case of a bitter ex-student or ex-wife trying to fit him up?'.
But if you ask people who were at school at some point with him (or current students), they'll say 'Nah, he's creepy and he never talked to the girls' faces/was always hanging around the boys' changing rooms at the end of PE' and there was always at least one employee at any given period who for no apparent reason, just couldn't stand him and would do anything they could to avoid dealing with him.'
They might not have been targeting the actual kids in that school - it's all too common to find out that somebody with allegations made against them regarding teenage girls has been employed in a boys' school, or worked at a primary but predated upon 15 year olds - but they set off the alarm bells with the kids in any case. And he's saying that statistically, there will be one or more at some point of a child's time in education - they do gravitate towards activities that put them in close contact with kids, it's not always to actively abuse but to get that Pillar of the Community moniker and a position that is so well regarded that 'It can't possibly be true' comes into play.
He's saying listen to the kids because they are in a position where their instincts can very often be right, it can happen in any school and it's foolish to assume 'it can't happen here' - a fundamental of child protection.
Some of his behaviour could also be partly explained by being abused as a child, too - especially if he wasn't believed or knew that he wouldn't be. And then he's encountered the same type of man around both of his children - and, as he advises people in the article, he has believed them and it's been acted upon, rather than ignored or dismissed.