My opinion is yes, this webinar is relevant even if you want learn PI AF SDK because it can help you see the big picture of both libraries. On the other hand, the details of the PI SDK functions won’t be relevant for you.
If I were you, I would first start watching the webinars from the auditorium about PI AF SDK 2.5 (like Builders's Café Webinar Series: Programming with the PI AF SDK Rich Data Access) and read some hands-on labs from vCampus Live! 2013 (Overview of PI AF SDK and Migrating from PI SDK to AF SDK) which could be downloaded on the vCampus Download Center under Extras category.
Hope this helps!!