No DQ.
After the RO issues the "If you are finished unload and show clear (8.3.6)" command the shooter can still fire. If the RO gets to 8.3.7 "If you are clear, hammer down, holster (8.3.7)" then the shooter may not fire and doing so would be a DQ under 10.4.3.
In this example, just because it surprised the RO doesn't mean it was a DQable offense.
if the " if you are clear, hammer down, holster " has been given, competitor sees a target that was not engaged can he or she re-load and engage