Under the html spec, noopener should be used to prevent the new page from being able to access the window.opener property and ensures it runs in a separate process. This is a security thing.

The noreferrer option includes the noopener settings plus hides referral.

There is no need for WordPress to add both of them.

From the spec: “It indicates that no referrer information is to be leaked when following the link and also implies the noopener keyword behavior under the same conditions.”

Source: https://html.spec.whatwg.org/multipage/links.html#link-type-noreferrer