Do you think this orangutan had an actual reason for doing this, or was he just being an asshole?

My daughter took her four year old twins to the zoo. They were looking at the orangutans. The biggest one was just lounging in his hammock. Nothing much was happening so Savannah looked away for a moment. As soon as she looked away he suddenly sat up and grabbed a swinging rope.
Corrie said, “Savannah! Look!”
Savannah turned her head just as the fat, 1000 pound, fat, blubby, obese orange guy (no not that guy. This was an actual orangutan) swung toward her and SLAMMED into the plate glass right in her face! It startled Savannah so bad she fell off of the seat thingy that runs in front of the enclosure and fell on the ground.
She laid there for a second, stunned, then yelled, “Oh SHIT!! THAT was unnecessary!!”
SHE’S 4!!!
Corrie TRIED to admonish her for cussing but couldn’t seem to find find the words between her gasps for air!
Then Savannah stormed out of the exhibit darkly muttering things about “Stupid monkeys” under her breath.
I can’t stop laughing at this! And I have to ask you, my little one, is there a time when it is actually necessary for a full grown, alpha male orangutan to body slam a plate glass window just to scare the crap out of a little kid??

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I wanted to share this story with you, but by itself I didn’t think it was conducive to a question or discussion. It was just funny.
But then I got to thinking, Why Savannah? Corrie said there were a bunch of kids there, in front of the exhibit. Some were on the same bench as Savannah. Her brother was just a few feet away.
And why did he react the moment Savannah looked away?
Like all higher primates, they aren’t stupid. They have reasons for the things they do, even if they are reasons that don’t make much sense to us.

I know all the arguments behind keeping animals in zoos, and how frustrated they must get, and I do sympathize, but if we could save that for a different discussion, and just focus on primate behavior, and their similarities to ours, I would appreciate it.

Have you ever been in a situation where a primate from a different species, or an animal of any species, singled you out or someone you know? Any idea why? I actually have a story of my own, but it’s quite embarrassing. I’ll tell it in PM if anyone is interested.