Honestly dont think you can put too much blame on them. There a many diseases/parasites for everything in this hobby that a LFS would have a very hard time to negate. Best way to go about everything this point forward is to QT everything including corals. If you bought corals that had the pyramids on them that could of been it at all. Anything wet that you added to the tank from another tank.
Pyramid snails arent talked about that often. I never heard of them during the year worth of research I did prior to starting the Saltwater part of the hobby. Luckily it was the only thing besides a zoa eating nudi I ran into (disease/parasite wise).
Having two separate QT tanks is a great thing to have in this hobby, one for inverts and one for fish.
People have supposedly knocked out pyramids while keeping the wanted snails in the Display and brushing off the pyramids. I feel the best route is to remove the snails altogether and starving the little buggers. Also you wont have to search for every one of your wanted snails to clean them off every other day. I am also not sure if locating the snails into the sump would help.