The reason being they are both Fertility goddesses and both of them have to do with goats and this is a lovecraftian horror then Shub-Niggurath nicknames are The Black Goat of The Woods, All-Mother, Mother Goddess, Lord of the Woods, The Mighty Mother, The Goat with a Thousand Young since Shub-Niggurath has a few nicknames that have mother in it it could mean that it is Shub-Niggurath