Draco couldn't help but notice that Dumbledore - Albus - hadn't answered his question. Did he just not want to say, or was the luggage somehow more important, in Albus' reckoning? Dismissing that for the moment, Draco asked the more pressing question.
"Why not?" Draco didn't exactly think he had good cause so much as strong curiosity. If the journals were anything to go by, there was nothing at all in the luggage, and it had been so light when Draco had dropped it on his bed that he assumed that to be true. But then why get a key? And why only one key if he had so many other pieces of luggage? Something or someone wanted him to open that bag. But then, why would Dumble- Albus warn him against it, if it were innocent?