Here is the way I would personally take that. I, personally, from my understanding and experience with past Beta Tests would read that as them stating that Wave 1 is done, that they basically have everyone they want or need for Wave 1 of the Beta Test.
I am 99.999% sure that there will be additional waves as they move into testing new features and such. The Beta is still very early on.
My suggestion is to take that statement as nothing more than saying that no more wave 1 invites are going out and to consider past WoW Beta tests.
Thank you Alini for sharing that post, I really appreciate it 