My guess is this. When you diputed it with the original CA it was already sold at that point and couldn't verify and if they can't verify it is deleted. Now that it is in the hands of another CA, they can report it if you still owe on the debt. The other CA can't report anymore since they aren't assigned to the debt anymore. But yeah, if you still owe the debt the new CA can report it.
Also this goes along the lines of if you dispute a debt that is still owed and the OC or a CA doesn't respond to the investigation within the CRA's time frame, then yes it will come off. But that doesn't mean it can't reappear the next reporting cycle if the debt is still owed as long as it is still within the 7.5 reporting time.