When the embed whitelist selector site setting is not configured you will often get the correct post content pulled to Discourse. It depends on the content of the embedded post. For example, I create a lot of test posts with the content “This is a test, this is only a test.” Discourse is not able to retrieve that post content from my WordPress site unless I configure the setting. If I create a longer post, Discourse finds the correct content when the embed whitelist selector setting is not configured.