That was my initial thought as well. Having the word shoggoths on the card instead of shoggoth made it unclear for me. Thank you.
Yeah, it was probably written with full generality because they weren't sure if any other Shoggoth-summoning effects would be introduced in expansions. They did introduce one that lets you get a Shoggoth another way in the Fall of House Lynch, but it happens not to work in 1B.
(The most obvious example of this future-proofing is the Crucifix item, which has a special interaction with vampires. Mansions of Madness has no vampires in it at all.)