Does the preview API query for published data even if preview flag is true?

If I make a query like this:

query {
    peopleCollection (where: {name_contains: "z"} preview: true) {
        items {

It seems the data that is returned by the query is not what is currently in Contentful. For example, if the last published version of this person has a name that DOES contain “z”, but the changed (and unpublished) newest version of person does NOT contain “z”, this query will still return that name, even when preview is true.
So my question is: Does contentful preview API GraphQL only query for what has been published?