To me, direct link means a link that will send me directly to the posts on their instance (i.e. a direct link to the Star Trek website will be https://startrek.website, not https://myinstance/c/[email protected]).
Unless I'm somehow misunderstanding what direct link means here, which I might be? It seems more intuitive to me that the bang syntax would keep you inside your instance, not leave it.
And yeah, using ! is known as bang when used in this sort of context!
That figure includes all known users in the federation with Lemmy. The users on kbin instances is a lot less, I'm not sure how to check that though myself.