i imagine you guys didnt have that in mind as a way to attack the stygians. just dismantle their castle and steal their bricks.
edit: only in admin mode, so less of a bug than i thought 
Considering admin mode can spawn anything, having an admin “steal” materials from an infinitely respawning NPC base isn’t all that much of a problem.
you are correct. when i first noticed it i didnt think about my being in admin mode to test stuff out. for the player experience, this has no effect. so this probably isn’t even a bug at all, just a byproduct of whatever system they have in place to build the base on the fly and assign it to the fake stygia clan
There are few items inside (decorations) that I found to be “decayed” and I could dismantle, but those did not have a serious impact and I could not get resources back from them.