I can't really see how the Super Mutants would trip a lockdown security system that wouldn't have activated by the station being in a nuke zone

. Specially since there is a terminal in a Station maintenance room that explains that if the power goes out, the station will enter lockdown and can only be lifted by making the generator work. I don't think Super Mutants could make the power go down 200 years after the bombs fell in a way that the bombs or time wouldn't do better

.
Also if the lockdown had happened "recently", the train information board wouldn't have stopped while saying that trains have "arrived" or are "on time". And then continue to update itself to "destroyed", "delayed" and "9999hr late" once the player restores power and lifts the lockdown

(and let's be honest, that train information board is AWESOME!

) .