@Tristan's answer to What are the orbital mechanical consideration behind hand-launched nanosatellites from the ISS? includes:
If you launch nadir and retrograde, you will put the object into a lower energy orbit such that, barring ISS deboosts (they do happen, but they are rare), it will never again intersect ISS's orbit. Launching prograde, zenith, or out of plane will set you up for a potential recontact scenario.
This was confirmed again in his answer to What are the orbital mechanical consideration behind hand-launched nanosatellites from the ISS?.
Now the GIF included in the BGR article Watch the International Space Station poop out a tiny satellite that will search for (missing) matter which shows a 3U cubesat ejected nadir and retrograde.
This begs the quesiton: Are the cubesats deployed from the ISS always directed "nadir and retrograde"?