Sorry if this sounds super like, nerdy I guess
purple and yellow just looks nice and spooky together, it has nothing to do with the UwU non-binary flag. There's plenty of cisgendered characters who use the "nonbinary flag color scheme" because it just works well for ghost like or spooky characters, like snatcher from a hat in time, he's still a cis male.
You know why purple and gold works well for spooky characaters. Purple is a common color used for ghosts, the yellow is just used for contrast, because it is purples complimentary color and doesn't clash as easily as say, purple and red (although purple and red can make a good color scheme if done right)
It always annoys me when Tumblr slaps a label on a character just because they're clothes have some colors that match a flag, that's like me saying McDonald's is part of the Soviet Union because they have the same red and gold color scheme.