I’m going to redirect you to an article I recently posted (written by someone else) which directly covers this question from the perspective of someone who worked with gorillas, (as well as many other questions about the gorillas behavior that day).
But first, I’d like to say that while I have not worked directly with gorillas, I have worked with chimpanzees, and have read extensively about primate behavior. In my opinion, yes it is possible he was mimicking human behavior (I assume this is what you mean by aping) when he pulled the boys pants up, and yes he may have seen parents do this to their children…but he was not mimicking the care of a human child in any emotional or protective/parent-like way.
It’s also very possible he was simply propping the child up before dragging him around.
What is very clear is that he was using the child to “display.” Displaying is usually a benign action, a show of sorts rather than an intent to harm, in order to assert dominance. They use props like large sticks—or, in captivity, toys—that they throw around while other members of their troupe watch on.
It is also clear that he was reacting to the peoples fear and screams.
So whether or not he was mimicking human behavior by seemingly gently handling/fixing the child clothes prior to harming him, or simply preparing to use him as a part of his display, I do not believe there was much of a chance he was ever going to view that child in a protective or parent-like manner. He might have simply viewed him as a plaything. He might have very well known that he was causing a human harm, and done so out of pent up aggression and a misguided assertion of dominance. And, under very different circumstances, perhaps he might have let the boy be. But no, he was not aping a care-giving role, not in any emotionally rooted sense. Not in my opinion, anyway.
Here’s the link to my previous post with the article: