Not all aspects of Eridian physiology are explained, but much can be inferred based on those that are.
Eridians have a sense of taste likely for the same reason humans do — to determine what is or isn't safe to eat — but Rocky says the quality of food isn't important to them. Consider that Eridians are monostomes. And they eat at the same time they defecate. If your mouth always tasted like poop when eating a meal, there probably wouldn't be much to gain from contemplating the flavor.
Having a sense of smell would be nice, but it's easy to guess why Eridians don't. Their bodies are protected from the environment by being generally enclosed, and their "breathing" is just for temperature control, it puts nothing into their systems. An olfactory organ would be a dangerous hole in their armor through which toxins or infectious agents could enter. It would introduce far more danger than it's worth.
So they can't see, can't smell, taste appears to be minimal, have solid rock for skin so their sense of touch is limited, and there's no mention any other kind of sensory inputs. Small wonder their hearing is so highly developed, it's literally all they've got.
Rocky's behavior when eating — tearing his food into tiny pieces and laying them on the packaging — can also be explained by the above. Since they have no teeth or digestive tract, they need to put more work into breaking food down into pieces their stomach can manage. And since their bodies don't have a means of attacking internal pathogens, keeping food in a sterile environment would be even more important to them than it is to humans.
The disparities in technology between humans and Eridians makes sense in light of their differing environments. Eridians don't have the same incentive to invent computational devices since they are already exceptionally good at mental math and information retention, whereas the crushing gravity and pressure of their planet makes materials science a much higher priority.
