Ok so I just saw a video of a chimpanzee who was released after having treatment, and he chimpanzee hugged the zoologists. Was this for the same reason we, humans would hug? Does their hugging mean they are happy? Or is it just something they do for no reason?

Chimps are driven by the same emotions we humans have. Hugging would definitely mean a feeling of contentment, happiness or just wanting the warm contact. Chimps are removed from us by only one chromosone, so they are the closest relative to us on the evoluntionary scale.