There are 4 types of cards - units, specials, artefacts and stratagems.
In each type there are different tags. For example,
Units have 'human', or 'elf' or 'beast'
Specials sometimes dont have a tag, others have a faction-specific: NR has 'warfare', SK has 'raid', ST has 'nature',
but there are also certain tags, like 'Alchemy' or 'Tactic', that are not faction exclusive but are more associated with a certain faction (SK and NG respectively, for these last i mentioned).
Honestly it is pretty confusing how "special" is the name of the card type, in any other game the "special" cards would just be called spells.
So just think of it this way: Dudes you put on board are "units", spells you put into play are "specials", and cards you put into play that don't have a power level by themselves but which have abilities are "artifacts".
Really not sure why spells are called special cards, maybe cause some of the effects are not very spell-like (a bomb clearly isn't a spell for example). But in that case it also wouldn't make sense for Locations to just be considered Artifacts, oh well.
Because "special" is not the same as "spell" and there is a completely separate tag for "spells" thus they can't use it for this. Also stuff like "Imperial Diplomacy" is certainly not a spell as there is no magic involved in "diplomacy", we have diplomacy in real life and it works completely fine without any magic. [...]