Like here's the thing, codependency isn't a diagnosable psychiatric disorder. There's not even a clear cut definition on what it means, but even by human terms outside the world of pop psychology codependency usually means one person in a relationship is enabling the other's negative behavior (usually addiction), and there are arguments to be made that the concept itself pathologizes normal human behavior.
I don't think "the species that joins a hivemind whenever they want to talk science" really has a cultural concept of being too dependent on someone. I agree with James Ortiz's take that Eridians are like, never alone, or if they are alone it's not for very long. I think that the Eridians don't leave Grace alone while he's up in the Mary waiting for the dome to be built, like even if Rocky isn't there they always have someone in the ship with him.
And that does a couple of things, for one I think they get kind of confused when Grace gets anxious and snappy and depressed and basically just turns into a big ball of conflicting emotions whenever Rocky's not on shift, because like, okay if you and Rocky are friends and we're your friends what's the problem? For another, they're very perturbed by Grace's insistence that he not have an Eridian in the dome with him all the time and that he does actually need to be able to do things like climb the stairs to his house by himself or go make a taumoeba shake at three am, because what do you mean humans don't just help disabled humans up the stairs (and that launches like a whole thing on Earth accessibility standards). Humans are so strange, so individualistic, and their human says his culture is much more individualistic than all the others on his planet but even the most collectivist cultures on Earth don't hold a candle to what the Eridians have got going on.
So they're really weirded out when, a couple years after Grace is healthy and settled in the dome, Grace mentions to his therapist that he thinks he's too attached to Rocky, because by Eridian standards Grace is cagey and standoffish and only ever opens up the way they'd expect him to around Rocky, and Rocky is more attached than average but they've been chalking that up to the space qpr.
