One thing that will have thrown the author off the trail is that he is holding a fossil of the organic parts of the snail and that is essentially a cast of the animal, not the shell. They are known as Steinkerns (stonecore).

The insides get replaced by minerals, which harden, the shell dissolves, then the only fossil remaining is a mould of the inside of what used to be the shell.

So on a fundamental level, the headline is wrong. He did not find any sort of shell...