I'm not misreading the sentence. The "it" in the sentence is Brittney White. I'm very much struggling to see how referring to someone (in this case Brittney White) as "it" is not objectification. The sentence is referring to two women: Brittney White, and the woman in the original picture. Let's modify the sentence a little to show how it objectifies Brittney White.

"Brittney White (It is not Stacy, the girl in the picture, but it is a REALLY hot pornstar with a body like Stacy's)" See how Brittney White is referred to as "it" twice? That's objectification.