Eye contact being perceived as aggressive across species, including in humans, stems from evolutionary and behavioural factors. In primates and humans, direct eye contact can signal dominance, threat, or territoriality. This is rooted in survival instincts where maintaining a safe distance and avoiding confrontation are advantageous. In social species, interpreting eye contact as aggressive helps in navigating hierarchical structures and minimising conflict. This perception likely evolved as a way to establish boundaries and maintain order within groups. So, even though eye contact itself isn't inherently aggressive, seeing it that way helps animals and us humans promote social cohesion and keep things in line.
interesting read: https://www.psychologytoday.com/us/blog/vitamin-eye/200907/eye-eye-visual-violence-0#:~:text=Employed%20to%20send%20warnings%2C%20set,antagonize%2C%20coerce%2C%20or%20hurt.
Also, keep in mind that the "aggressive" interpretation is not solely due to a gaze/stare. There are still tiny facial expressions and changes in facial muscles that provide cues.