Thanks to everyone who pointed out that Nam is not necessarily annoyed with me personally (and I certainly hope that is the case, but of course I'll never know for sure). It kinda sucks that I'm now cut off from him on social media after 3 years, but it is what it is.
I can only discuss my very limited experience in this area, but specifically in the case of Joseph and Matthew, I had asked them in person if I could connect with them online, and they agreed. As for Nam and Nic, I happened to notice that they had numerous followers, so I took a chance and hoped they would let me join their virtual social circle even though I had never met them. That happened to work (and I ended up meeting them later), but I never dared to do that again.
I know I'm a little late to the conversation here, but I would not take it personally. He's not vindictive like that.