Unless the people that the OP’s friends intend these pictures for don’t have anything other than facebook. I’m guessing that’s a pretty common situation for a lot of people older than 40-50.
Is it possible his real name is common enough that someone using the same “real” name or using his same name as an alias has annoyed Facebook? I mean, they may have to allow for a plethora of Bill Smith’s, but if Russian Bots like to use, for example, legitimate-sounding Roger MacDonald or Fred Hernandez they may have a problem with people who legitimately have that name.
I believe the OP but am not seeing it in my Facebook world. I am on it to mainly follow my grown kids and more importantly my grandkids. Also my church. I have not heard any complaints from anyone on this so I have no experience in it either way. It would be frustrating though.
How about this theory:
The friend who’s being “encouraged” to join Facebook actually doesn’t want to, and claiming to have been mysteriously banned gives them an out.