If an alien were to visit Earth and observe human stress, they might find it fundamentally rather perplexing.
From their extraterrestrial perspective, they might see that humans often experience a lot of worry and tension generally, but oddly even when they aren't facing immediate danger or threats.
To the alien, this might seem strange because, in their world, stress might be reserved for serious situations where there is an existential (life or death type) threat.
They might wonder why humans don't always act as calmly as they do under pressure but are rather taken possession of by temper.
The alien might also be curious about what are the sources of human stress.
They could notice that it can come from various areas of human life like work, relationships, or societal pressures, but manifest itself in a similar way in each.
It might be of interest to the alien to assess whether the human reaction to stress helps resolve the source of the anxiety to hand or makes it worse.
The alien might wonder why concerns weigh so heavily on humans, leading to this thing called "stress."
They might be interested to see humans practicing relaxation techniques, engaging in physical activities like jogging or yoga, or seeking support from one another rather than internalising internalising the emotion, and even learn from this.
In summary, an alien's perspective on human stress might be one of mixed curiosity and confusion.