Adulterations vs Misbranding

Can someone please help elaborate this for me:

Simvastatin 40mg bottle labeled as simvastatin 20mg
○ Adulterated
○ Misbranded
○ Mislabeled

The answer on the answer key was misbranded; but it was my understanding that if the quality/potency differs from the label it would also be adulterated?

Please help :)