From the Jive side, the following is the default behavior of a Jive-X/N instance:
Default for Internal = Username is always email
Default for External = Username is never email
As such, the snippet might be reversed in the Okta materials you are referencing, or this could potentially be the expected design of their implementation. To confirm, I would recommend reaching out to the Okta team for additional information on their specific SSO integration or, if you are interested in integrating your Jive instance with an SSO provider our Professional Services team can also assist in scoping out the project and help set-up the integration. Please submit a case in your secret customer group here in the Jive Community if you would like to pursue this option and the next available support member can get an engagement started.