Astronauts Pull Off Risky Spacewalk
If you slowly push away from the space station, you won't keep moving away from it in a straight line, because you and the space station are both orbiting the earth. In 46 minutes or so you may find yourself passing by it again.
The parent actually has an interesting point but is simply bad at explaining himself, stop modding him down :)
1) The height of one's orbit is directly related to the speed - the higher the speed, the higher your orbit
2) If you push yourself away so that your earth-relative speed changes (e.g. forward or backward), you will get to a higher or lower orbit, and cannot get back to the station
3) However, if your earth-relative speed doesn't change (e.g. if you push yourself off perpendicularly), you will keep orbiting the Earth at the same height as before. So we'll have two orbits (ISS and you) with
a) same height and speed
b) slightly different angles
c) you were at the same point at some point in time
These orbits will keep intersecting in two points, the original point, and one right across the Earth, so it's actually possible to get back.