Omega lieutenant Price, who gets knocked up from a one night stand and Alpha Nikolai, who, to help John avoid the shame and judgement that comes with being a single parent omega, claims the pup is his.
That's his baby, yep, he and John got drunk then fooled around. Oops. Anyway, he's gonna be a dad.
John smacks him upside the head for it behind closed doors, the pup isn't Nikolai's responsibility and he shouldn't feel obligated to care for it.
Nikolai just smiles at him, that stupid, dopey smile, and asks if he can get the baby a little onesie with a helicopter on it.
Ironically, the pup looks like Nikolai when she's born. John chooses to ignore that the men he's attracted to all look similar to the pilot.