The Wikipedia article for the movie states that:
The original American release of the film shows Hammer and Velda escaping from the burning house at the end, running into the ocean as the words "The End" come over them on the screen. Sometime after its first release, the ending was crudely altered on the film's original negative, removing over a minute's worth of shots where Hammer and Velda escape and superimposing the words "The End" over the burning house. This implied that Hammer and Velda perished in the atomic blaze, and was often interpreted to represent the apocalypse. In 1997, the original conclusion was restored, where Velda and Mike survive. The DVD release has the correct original ending, and offers the now-discredited truncated ending as an extra. The movie is described as "the definitive, apocalyptic, nihilistic, science-fiction film noir of all time – at the close of the classic noir period."
For a more thorough (and thought-provoking) analysis of the entire film, including the ending, head to filmsite.
Essentially, which version is the 'definitive' version is open to interpretation. But based on the Wiki article and Tim Dirks' review at filmsite, the original, unedited version is likely considered the 'definitive' ending. Thus making the claim on your DVD correct. :-)
Regarding the false interpretations:
As the Wiki article states, "This implied that Hammer and Velda perished in the atomic blaze, and was often interpreted to represent the apocalypse." Essentially: the ending is not actually meant to represent the apocalypse.
A reviewer at Slate summarizes it quite well:
"Kiss Me Deadly ends in a fireball of allegorical power. But Aldrich isn't concerned with the narrative ripples of the final incendiary image or its literal consequences, just the raw thematic ingredients spewing into the atmosphere. The glowing Pandora's box (famously recreated in Pulp Fiction) could signify so many evils threatening our existence, from nuclear stranglehold to ideological manipulation, and the genius of Kiss Me Deadly comes in how it makes each an equally feasible endgame. Yet, no matter what Achilles' heel fits best, there's still so much moral ambiguity crashing with those parting ocean waves. Of course, it's Velda who summarizes this idea best: "They. A wonderful word. And who are they? They are the nameless ones who kill people for the great what's it. Does it exist? Who cares."
What seems to be at the heart of this ending, and indeed the movie, is nihilism.