Although I took the painful and long time to coordinate NATO and FIA survivors (which can be a pain in the rear), and filled a helicopter with a team of seven (me included, so six AI plus me), I got the Steam Achievement saying I chose to save myself.
Saving them was a tedious / long endeavor (for my first attempt).
This seems like a bug to me.
After over an hour of trying to save all those guys, without any saves possible, I could not risk the heli crashing from a dumb AI (though I am a terrible heli pilot myself).
EDIT : changed the "Severity" above to Text, since it is only that the Steam Achievement has a confusing or misleading description.
Hmm, I think I get it now :
SPOILERS - This Steam achievement is maybe related to choosing to meet Miller rather than go with NATO. If so, it is not a bug.
If the achievement implies leaving the island solo, then it bugged out on me.
Turns out I misinterpreted the meaning of this Steam achievement ("saving yourself" is triggered by helping Miller/CRTG instead of NATO). The text is confusing, especially as another achievement right beforehand it given for taking a side at the end...
But not a bug technically.