It must be either a myth or something else is up

[LGL]

...because Nico has not come out from her hide box for 2 days. Normally she comes out every evening, like clockwork.

This seems so out of her routine. I also tried to feed her and she refused to eat, but I assumed it was because I had taken her around town and she had been riding happily on my shoulders all day. My assumption was that the entire stimulus just caused her not to want to eat. I don’t know now with her not coming out of her hide.

My guess would be that her constant hiding is at least partly due to the outing. That was probably very stressful, especially if she was out all day and around town as you say.

But I wouldn't worry about the hiding. I have some snakes that are almost always under a hide and I have snakes that are almost never in a hide. Some extra hiding will just help her feel more secure.