That actually makes a lot of sense. If you see destroyed Town Halls, you could definitely imagine a bunker.
Not sure about gems... They seem like the ultimate form of magic in the game, as it usually takes time for some unknown being to create troops in barracks, but you add gems and suddenly they are made...Some form of dark magic?
In the beginning of the game (lower Town Halls), Barbarians are commonly used. They're pretty much used until Town Hall level 7 or 8, and even sometimes after that. Since they are so common, they're the same height as skeletons, and they both have swords/daggers, I think skeletons are barbarians. Now, you might ask, how can a witch raise dead barbarians on a battlefield if no barbarians were ever placed there/ever attacked/ever died? I think that since each player has used barbarians from the start of the game, that's why skeletons always come when enemy players with witches attack. So, if during an attack no barbarians die but witches are used, they resurrect barbarians from previous battles in that same location. For Clan Wars, the battlefields are not natural, but rather synthetic/man-made locations. So when the overall game created that battlefield and copied the base layout, they placed dead barbarians under the ground so witches would work (there were so many leftover from lower level players that they can always get some).

