I'm a librarian who loves anime, manga, and reading a wide variety of genres.
The Hrrubans didn't seem to need human help at all in order to build that bridge. I keep getting the feeling that this first contact situation is maybe flipped - like maybe the Hrrubans have been keeping an eye on humans for some time, realized that they (we) tended to shy away from any chance of contact with other sentient beings, and then purposely set things up so that humans would come across Hrrubans on Doona. Otherwise I'm not sure what to make of how calm the Hrrubans are about all of this, and how they seem to take every opportunity to carefully teach the humans stuff.
The urge to look up spoilers is so freaking strong. I wish I could stay home from work and read...