This doesn't fix the "misunderstanding humans" part, but this got me thinking about what different Weird Things could be.
Like, a civilization of small creatures that evolved on a planet in an extreme horseshoe orbit. The dream of indefinite suspended animation is real, but only for these guys. The waves of their colony ships are interspersed with various catastrophes, meaning that while it's not surprising when they reach a planet first, or show up suddenly one day, it's incredibly hard to predict their culture, language, tech level, and system of government.
An intelligence evolved from something much like eusocial insects. The fundamental aspects of sapience rely so much on the interactions between units, and so little on the unique characteristics of a unit, that, following the development of extremely miniaturized electronics, some colonies ship-of-Theseused themselves into entirely artificial bodies, using them to explore extreme conditions. For economic reasons, it often makes sense to switch back and forth between different chasses, including biological.
A species that has a similar level of transplant compatibility to humans, but has extremely plastic distributed cognition, meaning that amputations and transplants tend to result in the loss or gain of seemingly random memories, skills, or personality traits. Some traditions of ritual surgeries have resulted in individuals that claim to have firsthand memories of events that occurred generations ago, though they do not pretend to be literally the person that experienced those events. Some disturbed individuals believe that they have isolated the seat of personality, and form cults devoted to kidnapping and performing surgery to extend their own conscious experience at the expense of their victims. Any apparent success is generally agreed to actually be a trauma response.
A clade with a similar level of extremophilia to the memetic status of tardigrades. At least one species of them has, for some reason, developed sapience and tool use, and their ability to work in a vacuum makes them an invaluable asset on space journeys, if a bit lackadaisical with the environmental controls. Such arrangements are always temporary, as they eventually grow tired of the stifling routine of consistent temperature, pressure, and humidity.
A species(?) that offloads most of its adaptations to something like plasmids, which can be replicated and spread independently of the cells and bodies. Difficult experiences trigger a kind of tagged retrieval of plasmids between individuals, resulting in sometimes-drastic physiological changes in response to adverse conditions. A curious individual of this species came across a misplaced data-pad from an expedition, and somehow evolved sapience from first principles in its efforts to comprehend it.
Just need to tune the narrative significance of these to be commensurate with "humans consider the galactic standard of hard labor to be equivalent to a leisurely weekend project", or however we want to express humans being Freaks.
