as small as or as big as as

[dido4]

Q:Which is right of the two in the setence?
Is it a matter to answer the question from the test?
as small as a small pig or as big as a small pig
It's from a listening test. The original question and answer are below:
Mary likes to play with her dog Casey. Casey is bigger than Donny’s pet, Max. She is as big as a small pig.
(A) Max is much smaller than Casey. (B) Casey is fatter than a pig.
(C) Casey is bigger than Mary. (D) Casey is smaller than a pig.
The answer is (A)
Thank you

[Tdol]

It should be 'as big'- a small pig is still large when compared to most dogs.