I was running my treasures today and one of the spawning Ruby Djinns guarding the "Do Not Touch" in Forum Highlands dropped an Ancient Elonian Key for me. This is the first time I have ever seen a key drop in an area that couldn't be used in that area. Could this have happened because it was a spawned creature that dropped it?

Yeah, Margonites will occasionally drop Margonite Keys outside the RoT as well. It's rare, but it happens.