There are many reasons a fussy eater might dislike a particular food. It might smell bad to them. It might feel strange in the mouth. Sometimes, it’s just what I like to call “guilt by association”. I don’t like onions. Scallions are sort of onions. Therefore, I don’t like scallions. I don’t like ranch dip. It’s one of only a few foods that just the smell nearly makes be gag. I won’t be trying Cool Ranch Doritos anytime soon because of the association with ranch dip.
When trying to find new foods for your fussy eater, make sure you keep this in mind. They aren’t likely to like or even try something if it reminds them too much of something else they don’t like.