Your confusion is probably coming from the fact that there are 2 errors in the bottom deal description in Erdnase. Both refer to the 2nd finger when it should read 3rd
Hope this can help you a little, it was on Time warp with Dan and Dave. They film a bottom deal in slow motion. I don't know if it can be shown here, if not please delete this post.
The bottom deal in that video isn't taught in expert at the card table.
The ring finger, somewhat aided by the little finger, is used to loosen the bottom card. I dont think this counts as exposure as this information is freely available online.
Well, I didn't think it's exposure since they dont "teach" it, they just show what it look like in slow motion. That's why I wasn't sure if it was ok or not...