This sounds very unhealthy, why is he putting boundaries on a kid that is not even his?
Yes, that is weird. But he also doesn't mention the kid's age. Keeping a six year old off Facebook is reasonable. But if you keep a 14 year old off social media, you are basically turning the kid into a social outcast. For an teenager trying to navigate the awkwardness of puberty, the last thing he needs is some asshole uncle micromanaging his social interactions.
If you don't want your kids to hate you, then you should avoid using parenthood as an opportunity to impose your weird idiosyncrecies on them.