If you ever create a BTreeSet<String>, it will use String's PartialOrd, which is directly #[derive]d from Vec<u8>.
Ironically though, that should be actually more objectionable than ordering arrays by lexicographical order of elements, because the underlying code point order is pretty much useless for any other purpose than having some arbitrary deterministic order. Meaningfully ordering strings is an inherently locale-dependent operation, and PartialOrd has no way to take this into account.