It certainly could be new users? Here’s another example of a new user with a gray name.
I will just say that if someone has made a deliberate choice to highlight new users with grayed out names, I think this is an unfortunate color to choose!
When I first saw these names, I actually assumed that the grayed out name meant something like “since posting, this user has deleted their account, so don’t bother replying to them” 
If it’s meant to highlight new users, I would suggest a more prominent color like blue?