While I wouldn't say she's autistic, she's not just "shy". She has a somewhat weird way of thinking, so I can understand why people interpret her as autistic, or just want to see her as autistic.
I usually stay away from claiming a character is "coded", since just because a character has some traits of something, doesn't mean they belong to that spectrum. Not to say it can't be true, but I've seen way too many times where people claim that in an attempt to "own" who gets to define and interpret the character.