You are correct - the PhotoPass Shoot and the Honeymoon Portrait Session are two different things.
PhotoPass cast members are not professional photographers. But you can get the shoot and the images on disc for a lot cheaper than if you use Disney Event Photography Services for the Honeymoon Portrait Session, which is $310 for the shoot (which gets you 20 prints in an album and one 4x6-inch print of each image) plus $300 if you want to buy your images on disc.
So that's $610 (plus tax) vs. $149.95 (plus tax).