I don’t really care what they were. But as long as your pointing out what they weren’t, what were they? Advanced humans? Possibly, but once again, lack of caring. Spielberg didn’t make a good enough movie up to that point for it to matter, plus it was a Spielberg flick so I assumed aliens.
Just thinking of that movie pisses me off. Regardless of what you think of Kubrick and Spielberg they are (were) two totally different filmmakers. Why Spielberg thought he could even do the least bit of justice to it is beyond me.
Kubrick gave it to Spielberg. As you can see, he didn’t commit to it until after Kubrick passed away. And then he tried very much to make it like Kubrick would make it. So, it’s a little messy. But I don’t blame him for anything.