You're not dumb (and no-one is dumb for asking questions) - the chance for HSR is on top of what you win from the Super Rare table rather than replacing it. EDIT: Actually, I'm misremembering. If you succeed on rolling for a HSR, you'll only get the item from the roll (Cheese+Tom batta, Blurberry special or HSR) and not both the HSR roll item + Super Rare table drop.
Whenever you roll the Super Rare table, there's a separate roll for your attempt at the HSR. If you succeed, it then checks to see what tier of luck you have access to - if you don't have tier 4 luck then you roll a Cheese+Tom Batta. Then there's another roll and if you're successful then you get a HSR and if you aren't, you get a Blurberry Special.