Wow.
To give a more accurate version
@carkl3000 Faolyn offered a few different alternative saves. Most of those came from unique monsters in adventure books that I have not read or have access to. So, I admitted my ignorance in that matter.
The Demilich howl drops people to 0 hp if they fail the Con save. Sure, it could be "so scared you die" but... I'm pretty sure that most people aren't so scared of a screaming skull that it kills them. Feels like it really should be a magical effect, doesn't it? Otherwise a lot more people would be killed during Halloween. And it being a Con save seems more resolved around that 0 hp trigger.
Oh, and the homebrew I mentioned was Faolyn
fully admitting to a homebrew rule for things like seeing an army and getting the frightened condition. They said it was a "common honmebrew rule" if memory serves me. So, yes, in discussing whether or not there were any RAW examples of non-magical fear, I did not accept homebrew fear rules as an example. The Grung I accepted, because it was based on their mucus, making it a drug, not magic.