The wereraven's statblock includes the Shapechanger trait. The standalone statblock states:

Shapechanger. The wereraven can use its action to polymorph into a raven-humanoid hybrid or into a raven, or back into its human form. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It reverts to its human form if it dies.

As you can see, "polymorph" is incorrectly interpreted here as if it referred to the spell of the same name, when in fact it's used here (and in other lycanthropes'/shapechangers' statblocks) as simply a term referring to magically transforming into a different form. In both the physical adventure book and the statblock that appears within the adventure on D&D Beyond, the term is (correctly) not italicized or linked to the spell:

Shapechanger. The wereraven can use its action to polymorph into a raven-humanoid hybrid or into a raven, or back into its human form. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It reverts to its human form if it dies.

This error only appears in the standalone wereraven statblock. Since it's not intended to refer to the spell, the word "polymorph" should not be italicized/linked.