I dont think you're giving the man enough credit. I'm sure that Tarn was well aware of what electrum is, but its likely that he didnt originally intend for it to be in the game as anything besides a joke.
and if you dont get the joke, then you probably were not playing dungeons and dragons in the 80s (or prior). the idea (now a long standing fantasy trope) that different valuations of currency needed to be made from different elements / aloys (instead of different sizes of coin) is perposterous, and the fact that they had to dig up electrum as a mid-way value between gold and silver coins (when historically native electrum was more valueable than either) is pattently absurd.
hence why its a funny easter egg. but i guess only so if you were in the right demographic for Tom Hanks appearance in Mazes and Monsters to put a crimp on your social life.
edit: additionally, the "Dungeon Master" was a continuation of this same joke. I believe he was hard coded to like electrum, and he was the only noble with labors enabled so that he would work at a smelter or forge or whatever to make electrum coins. I dont know how it is now, but back in 2D I had to give the little bastard his own magma forge so he didnt keep crowding out my actual metalsmiths. The bastard got up to legendary like a lightning bolt, and he'd never get off that stupid forge.
see:
http://df.magmawiki.com/index.php/40d:Dungeon_Master their list of likes mirrors the currencies from original D&D. and as for the cloaks, well you probably dont need to be told that Tycho Brae's choice of formal wear for dungeon mastering isnt exactly an original concoction but rather a parody of a type.