Makes sense. The eyes are the most expressive part of the body, and I would wager it's a fundamental form of risk assessment to look at someone's (or something's) eyes.
I agree if your definition of 'expressive' is that of 'telling' and not deriving from
expression. Unless I'm a minority, I'd say many of us humans are not able to tell the expressions of the eyes for animals like cats and dogs, we decide if they're hostile by their posture and actions - such as a dog barking or a cat positioning itself to pounce. More simply, I believe we look for eyes because we mostly use vision to understand the world around us. If there are eyes, we then assess whether the creature is looking at us and, if it is, what its apparent disposition is - based on posture and actions. Eyes are a focal point for knowing if we're the focal point of the eyes.