A naturally acquired smoke ring (ie. no Tender Quick used to fake it) is a byproduct of good smoke flavor. The smoke is attracted to a wet surface. Since I did not use water in the water pan, routinely spritzing the surface of the protein until the bark is fully set will assist the protein in acquiring smoke flavor. The apple/white grape juice I used adds another component to the overall flavor profile.
Perhaps I should've stated that I was spritzing to promote smoke flavor instead of a smoke ring. Regardless, when done correctly you achieve both with the technique I used. Also, this isn't a KCBS contest (I don't know what IBCA, MBN & other have to say about smoke rings) and the reaction to my ribs' smoke ring has been overwhelmingly positive.