I own a cana apple snail the size of a baseball and she has eaten newts, mollies, guppies and shrimp but all were already dead. what you have is probablly a bridgesi. Petco sells many different types of bridgesi and call them mystery snails. i don't know what the mystery is but they too will eat anything. I doubt that your snail ate your fish alive but if it did and you still have it i'd love to buy your flesh eating snail.
I highly doubt that the snail grabbed a live fish, and if it was dark colored then it wasnt an albino.How long were the fish and snail in the bag? One of the fish may have gotten stuck in the bag while you where transfering them an gone by unnoticed?