I had the same confusion so here's my layman's understanding. They are defining capture/orbit as having negative "geocentric energy" which is a term of art no one else seems to use but I think is just a mathematical representation of the following:
> a temporary satellite is any body that enters the Hill sphere of a planet at a sufficiently low velocity such that it becomes gravitationally bound to the planet for some period of time. [1]
again stretching my understanding too far, I think this basically means that in the absence of other celestial bodies the satellite would be in a stable orbit, but that in reality after some time it gets far enough away that the sun's gravitational pull dominates and stops it from making a full orbit.