buffyp I saw that and wondered what on Earth the man was thinking of.
Firstly, it was drummed into us VERY HARD that our social media should be completely locked down and invisible to all but our close friends, and that this should not include either students current or past nor their parents unless they were actually long-term friends and trusted not to run their mouths.
Secondly, if he's posting as Joe Bloggs Headteacher of Littleschool he's effectively posting as the Head of Littleschool so what he's saying is official and therefore should be said on the school's own Facebook/Twitter/website.
Thirdly, and related to both, if one of my colleagues had posted anything like that even to their locked-down, readable-only-by-friends social media I would have expected them to be in the Head's office by halfway through P1 the next morning. I hope the Governors take a similarly dim view of this twerp.
Fourthly, if I were the OP I'd be looking for a new school for my child(ren) as I would not want their education to be overseen by a scientifically-illiterate, inappropriate, unprofessional nitwit who has demonstrated a total inability to assess risk.