I believe the team over at SBI then manually add that user in the memo to the SBI list in order for the program to then start up voting on the sponsored Steemian's posts.

This is all automatic now, but you have the right idea. Our helpful resources post is a good place to get started if you want to deepen your understanding.
https://steemit.com/steembasicincome/@steembasicincome/helpful-sbi-resources