A pet store lady told me that i could add cuttlefish bone to help add calcium in my snails diet.

Does anyone know if this is true?

LOL. That's what you do if you want to provide calcium for cagebirds... Snails get their calcium directly from the water. Which is why they have trouble developing their shells in soft and acid (low-pH) water.

Yes, cuttlebone added to the filter is beneficial to the snails. It will also help the dissolved calcium if you drop it straight into the tank, which is what I do as the brigs do enjoy chewing on the bone as well.