I think you are right. I hadn't considered that, and I don't think Harry has either, but while Harry was thinking that "destroying the world" meant killing all the dudes, the Death Eaters were thinking of the ground blowing up, and there were two of them, so their interpretation probably prevails.
As further evidence that the vow blocks killing all the people consider this.
The vow blocks Harry from telling muggels about magic and starting mass healing. At the time it blocks him the ideas he thought of were transfiguring nuclear weapons and plagues that could replicate before the transfiguration wore off. Neither of those poses any danger to "the world" but they pose great danger to the worlds people. Harry doesn't think of up quarks until after he has already been blocked. So the vow seems to be interpreted as killing everyone being the end of the world. Which is quite possibly how Harry understood it.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 119.
Plans for next chapter release:
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)