I am totally guessing but it's possible they're saying it to explain why the boy was sleeping in the parents' room--i.e. she didn't feel comfortable letting boy and stray sleep alone together the first night in case it was cujo kitty or something. Which also conveniently gives her somewhat of an alibi, since you'd assume the boy would know if mom got up and did something to the baby.
And to respond to someone else I forgot to quote, I think the kitten could be important. I know there's been speculation about where they found it and if maybe it was at the dumpster while disposing of something related to the baby or to give them a reason to keep the dog outside for the night.
Like everything, it's just another potential piece to the puzzle--hard to know what matters until more of the pieces appear.
And finally, re the person who posted about the 2-3 am antics of kittens, that IS interesting because it makes me wonder if the cat getting up could have woken either of them up.
Would be nice to know too if they found cat hair in the crib. I know adults who complain their cats try to sleep on their heads--could cat have gone to sleep atop the baby and unintentionally smothered her?
And not to forget the dog, I wonder if he was always kept out at night. That seems odd to do just because of the cat--they could have just had them sleep in different rooms if she was worried about fighting or something.