Not defending this person in particular, but you should take a look at how anti-LGBT, including at the government level, most countries are in Africa. Maybe a decent number of them do regard seeing homosexuality as PTSD inducing.
There are several places where they legally can and will kill you for homosexuality.
The existence of anti-LGBTQ wasn't where their argument was leading to though.
Their line of logic was that our society moral values are but social construct, that change from place to place and with time, therefore being exposed to sexual violence, child abuse, gore etc. is PTSD inducing only because we're examining it through our limited perspective whereas it's quite possible that all these things those FB mods were exposed to can be perfectly normal in some cultures.
I wanted to see where that argument would lead them to, as in, what kind of people would FB should have hired that would be resistant to all these horrible stuff, but other than to let me know that in fact there are such cultures, I never got a straight answer out of them.
There are several places where they legally can and will kill you for homosexuality.