In keeping with the main theme from Season 1 of Scream Queens, Season 2 began with a mysterious and murder-happy birth of a mysterious baby. The baby's father was then murdered and thrown into the swamp, and whoever the baby is is the main Green Meanie suspect. Is Dr. Cassidy the hospital baby on Scream Queens? It hasn't been confirmed, of course, but he definitely could be.
When Zayday and Chanel Number 5 went looking for the mother of the baby born at the hospital on Halloween night in 1985, they went with the full expectation that Chamberlain was the baby. After all, it makes no sense that he would choose to work there at all. Candy Stripers aren't even really a thing anymore. When they found out that the "missing" Billy, who everyone knows was murdered and then thrown into the swamp, was a black man, their suspicions were all but confirmed that Chamberlain is the baby, and therefore a prime suspect as the Green Meanie. It all makes sense. Except, at the end of the episode, our beloved, beautiful, possibly un-dead Dr. Cassidy came home to the woman we know is the mother from 1985 and he called her "mom." Cue the horrified gasps.
The mom told Dr. Cassidy that some people had come asking about him. Well, not "him" exactly, but her baby. So that's a wrap, right? He's definitely the baby from 1985 and therefore definitely the killer! Well, maybe. First of all, who says that the baby is definitely the Green Meanie? Yes, it seems like that's the most likely answer, but hasn't the show done that before? It would be completely within the usual tone of this show to completely subvert that expectation, probably with a chilling put down of the Chanels by Dean Munsch.
We also cannot say for certain that he is the baby. Yes, the way the mom put it made it seem like he certainly is, but I wouldn't put it past the writers to find a way around that too. Maybe Dr. Cassidy actually is a vampire and he's really Billy the husband and mom is just a cute pet name for her. Or something. I'm not saying it's likely, it's just an idea. The point is that we don't really know what's about to happen. All we know is that we can no longer trust Dr. Cassidy.