Before, we had Nokia Camera Beta, and Nokia Camera. Now beta has been closed. Microsoft have replaced Nokia Camera by lumia Camera, and the Beta by Classic (in terms of GUID).
now to answer your question:
A) Devices which will receive Lumia camera v5 have Classic, which will be the latest of the 4.9 branch. A kind of fallback if you prefer. When Lumia Camera is updated to v5 (like it happened lately in France for the 830) these people have 2 UI, the old one (Nokia Camera like) and the new one
B) But for older devices, Classic doesn't exist, as Lumia Camera on these devices will be restricted to the 4.9 branch.
That is why on my 1020, Beta hasn't be updated to Classic (but removed from store). On older devices, it wouldn't make sense to have twice a 4.9 version, this would be redundant.
They are redundant as well on the 930, 1520 and 830 now, but soon when Lumia camera v5 is released for these devices, the existence of two Lumia Cameras will be totally justified.
I hope it's clearer now
PS. The latest WC article on the Lumia camera update (126.96.36.199 IIRC) is wrong about what is classic and not classic and despite my correcting in comments, they don't feel like correcting their article. So be it.