The moment you start to wonder about the original Predator's true intentions comes when its on the rampage through the science labs where it was initially kept captive. It cuts a bloody swathe through the scientists, including Jake Busey's completely pointless character, but then when Casey manages to half-escape but is forced to take all of her clothes off for decontamination to get the doors to open (yep, that happens), it stops.
From the way the scene is filmed, with Casey crouching naked in the decontamination unit and the Predator looming over her, it lools very much like it doesn't kill her simply because she's naked and female. Which makes no sense in either case. It also makes it seem briefly like the Predator becomes a human ally because he fancies her?
And then later when the Predator escapes, there's a moment where it's going to kill McKenna, but she shields him and the Predator refuses to shoot her. But it WAS going to shoot McKenna. So what gives? You'd think that she has some higher relevance that we'd find out, but there's just no such thing. Instead, the only explanation seems to be the most ludicrous one: that the Predator has a crush or something.