You're welcome Nick!
The List I am talking about is their Email/Contacts List (I think he used MailChimp).
So someone fills out his Opt-in Form (he's launching a new website, so he asks "If you want to know when the site goes Live, give me your name and email address"). He is building his mailing list that way.
All the email services (i.e. MailChimp, Aweber, 1ShoppingCard, etc.) have it where when someone "Confirms" their email address (which means they clicked a link in an email that was sent to them after the filled out the Form saying "This is a real email address" and "Yes, it is OK for you to email me" - Important because you don't want to ever be flagged as a SPAMMER or someone that sends unsolicited email), you have the option to send them to any Page (automatically). This is called your "Thank You" Page.
Most people literally say "Thank you for confirming you want my information", but instead, this is where he sent me to his Facebook Page (in lieu of a 'traditional' Thank You page).
I hope I answered your question

If not let me know.
Best