In Amy Poehler's new book "Yes Please" - Amy writes about Tina Fey's impersonations on Sarah Palin and says that Tina explains it in her book?

..... that Tina explains more about her Sarah Palin impersanations in her boom, Fifty Shades of Grey.

I think that Amy meant to refer to "Bossypants" which is Tina Fey's book. Obviously Tina Fey didn't write Fifty Shades.

So my question is- was this an editing error in Yes Please or is there a joke that I missed out on? Which is totally possible.

Please let me know if you know the answer to this. It's left me very puzzled!