This is misleading.

> Some Dropbox customer accounts were hacked too, but this was apparently an unrelated matter.

Unrelated how? What I read was: "Our investigation found that usernames and passwords recently stolen from other websites... A stolen password was also used to access an employee Dropbox account"

This article dangerously leaves the impression that an intrusion was made into Dropbox's system to access the employee's account, and possibly an admin interface. In reality Dropbox let a spammer with a valid email and password look at someone's files.