I've seen about three posts between SE and Workplace where the username of the poster is greyed out/plain text. Please what does this indicate?
This means that the user does not exist on The Workplace.
This probably happened because the question was migrated here and the user who asked the question did not have a linked Workplace account.
If the username is an anonymous username (such as user01234), then it can be because the user was deleted. In this case, I have seen cases where that number is the former user's site user ID.
While Nick is correct that migrated posts may contain greyed out usernames for users who do not exist on the Workplace SE, there is currently a post by a user where there is no migration message. There appears to be no evidence that the post came from somewhere else from what I can tell.
I also recall this reported as a bug elsewhere, as someone else on another Stack Exchange site reported seeing a greyed out username on a new post that had not been migrated.