For some people green and blue are basically the same color. Lot of people actually, and in some old cultures they didn’t even have separate words for green and blue. Anyway blue (or rather various shades of blue) and orange are opposites on the color spectrum. This is nature, this is light so it’s not something people made up, just observed. Even if you’ve never had any formal art education or training or never even saw a color wheel in primary school you’ve seen this just naturally at some point or another, like you’ve seen a rainbow before or light refracted in glass or water or whatever. So occasionally you might mix up colors in particular opposites just because your mind is flipping them about. Kinda like a very mild dyslexia maybe, but for colors