Listen to these songs- listen specifically to the guitars:
Some of it for sure is the way the bass is played, not just the exact tone knob setting. Mills of R.E.M. plays with a pick for sure- unsure about the Shadowy Men from a Shadowy Planet bass player. Regardless, the guitars all sound incredibly similar to me- I'm unsure what the sound is. A style, surely, but also reminicent of Peter Buck's favorite guitarist (at least in the early days), Roger McGuinn.
In "Stumble," Buck's guitar playing relies more on tiny arpeggios- it's the hallmark of his early sound for sure.
I thought perhaps this "sound" I'm hearing had more to do with studio technology but listening to other music from the era, this is unlikely the case- it's what's being fed INTO the recording equipment that's making the difference. It's light- tinny, almost. In "Trail of Tears," there are definitely more full chords than in Buck's playing or the Kids in the Hall theme.