Nick is less concerned with the fact Muscovy is clinging to the notion that Rey is his mother and more with the part where the kid keeps using that word to begin with. He's seen how Rey reacts to family: she wasn't initially warm on the idea of Nick using the term to describe the two of them, as though he was making a mistake by even considering her a friend. Her own mother -- the first person to have loved her, by Rey's admission -- was a touchy subject. And then there was the man Nick had become in her dream -- her father; she'd attacked him on sight with more ferocity than a hungry feral without so much as a second thought.

He's seen what happens when Rey gets frustrated, when she finds things are out of her control. It's one thing for Nick to risk his own welfare handling her; it's another when someone else is in the picture, especially a child. If this kid calling her Rey mother and following her home has rattled her bones this badly, then it's easy to assume it'll only get worse, at least until she's had some time to parse it out in her head and figure out that he meant no harm.

Of course, there's bound to be more to it, Nick thinks. Rey wouldn't lose her cool that easily, would she?

Whatever the reason, Nick sets out to protect the only family he has. He glances over his shoulder as she cuts herself off, his suspicions confirmed, concerns bolstered. "I wouldn't dream of it," he answers, getting to his feet, "but let's talk outside for a minute. Man-to-man."