To be fair Hannahause, his article was quite openly for his 'mates' back home - it was written for a German paper.
Actually I think it had a genuine purpose; it is increasingly common for better-off German families to send their children to English schools for at least a year, and they have no feel for what things are like here. When you add social media into the mix - which no parent of teenagers grew up with themselves, it's a different world.
There is no parallel in Germany for a super 'elite' boarding school - even where private schools do exist, they are much more low key in what they offer in extracurricular activities (I spent time in one). Also there was less of a 'cool gang' mentality - and definitely far, far less drug taking than at my English private school. That's not something that any number of open days would really reveal.
Anyway, why shouldn't he share his experiences? His opinions aren't invalidated by the fact he didn't take his children out. People make parenting mistakes; very few people are brave enough to admit it.