Journey's End question

This afternoon, Our ABC replayed the "Journey's End' from DoctorDavid's time in the series. This is the second part of a two-part story where Davros tries to destroy the Universe.
Why Davros might want to destroy the Universe (including Himself and the Daleks, I guess) is beyond me .... but, maybe, a topic for a later discussion.
Anyway, what I picked up today was, near the end, .....
Quote
[Vault]
(Explosions are starting to wreck the Vault.)
DOCTOR: Davros? Come with me. I promise I can save you.
DAVROS: Never forget, Doctor, you did this. I name you. Forever, you are the Destroyer of the Worlds!
(A wall of flames leaps up and Davros gurgles his last scream.)
CAAN: One will still die.
End Quote
Do we ever find out what Davros means by The Doctor being "the Destroyer of the Worlds"?? I mean, all the worlds were returned to their original spots by the use of The Magnetron, leaving just The Earth to be towed 'home' with The TARDIS.
So how is The Doctor "the Destroyer of Worlds"??
--
Daniel