We know a few things about the pfhor's biology: they are adapted to low-gravity environments, have a metabolic process fueled by a yellow liquid (yellow when exposed to oxygen? They still bleed yellow in vacuum), and have evolved trinocular vision, whatever that's like.
Their thin, gangly appearance seems appropriate for low-grav, but do they thrive on the surface of their world, or is life mostly in caverns beneath the surface? Their spaceships are dim, but maybe that's because they absorb some light in the infrared spectrum. Their grey pigment suggests their skin absorbs as much light as they can to survive in dark, cold environments. Perhaps underground. And we can expect tall, wiry plants at the surface, and maybe some giant, long-limbed, hairless beings that survive in an environment with a weak ozone.
On Earth, two eyes dominate natural selection, with one notable exception... spiders. Spiders have 8 eyes, and they spin webs and climb around surfaces where up and down doesn't have much meaning and it's useful to have a wide field of view. Where the human-build marathon is angular and boxy, Boomer's corridors are curvy and have almost no lateral symmetry or cohesion. Perhaps they could walk around walls and ceilings of their underground caves without gravity giving them much of a problem, and the third eye gives them better perception in more spherical environments where fellow pfhor may be walking along surfaces that are not all flat or on the same plane.
So how did their environment make them a slave-trading, war mongering species? We know they lay eggs, coexist with multiple genuses that form castes (try to think if neanderthals lived alongside us), and uh... have multiple brains, maybe? They may be linked to form a whole brain like our hemispheres. They might reproduce fast, and they stole a lot of their technology. Perhaps they were on their way to overpopulation, and colonization via FTL theft was their only way out of extinction.