I don't have an answer to your point (pick one of the several good options already provided), but I want to mention that you've made me realise something else about the episode:
From a Watsonian point of view, the TARDIS probably couldn't have done that (quite apart from whatever external alarms and guards there may or may not have been) if the Doctor hadn't disabled the safeguards earlier.
From a Doylist point of view, I wonder if the whole business with the planet at the end of history, where TARDISes never go, was at least partly a feint to make people go "Oh, so that's the consequence of the Doctor disabling the safeguards" and not expect what happened next.
no subject
From a Watsonian point of view, the TARDIS probably couldn't have done that (quite apart from whatever external alarms and guards there may or may not have been) if the Doctor hadn't disabled the safeguards earlier.
From a Doylist point of view, I wonder if the whole business with the planet at the end of history, where TARDISes never go, was at least partly a feint to make people go "Oh, so that's the consequence of the Doctor disabling the safeguards" and not expect what happened next.