In the early episodes of DBZ, King Kai tells the story of what happened to the planet Vegeta. It's guardian was a good man who became disillusioned with what the Saiyans had become and called down a storm of meteors to destroy the planet. That's the story King Kai tells Goku. However, during the Ginyu Saga and Frieza saga, it's revealed that Frieza in fact destroyed the planet. Did King Kai not know this(I doubt it since he seems fully aware of who Frieza is and what he's done in the past)? Or was he sparing Goku that information so that Goku wouldn't feel pity on the Saiyans he was about to battle?
The episode to which you are referring is a filler episode according to Dragonball Wikia. In the manga, the meteors were considered natural until Dodoria confirms that it was Frieza and the Anime follows along.
I don't remember if the anime and manga were running at the same time or close to it with DBZ, but if they were, it was probably just a goof on the part of the anime that got corrected/retconned later when that chapter of the manga came out.