A similar kind of observation made a profound impression on me some 30 years ago. A team of primatologists filmed Macaques in northern Japan. A female had two consecutive baby loss, the second one at least being stillborn. She successively acknowledges the death, takes care of the newborn as if it was alive, hit it furiously on rocks in despair and then again care for it, carry as if alive, get angry at it and so on. Her behaviour displays of acting as if knowing it's not, in this case in a pathological way. (She ends up being rejected by the group.)
Despite the Bonobo case being even more striking an example of being able to do as if, both shows that the behaviour is not unique to humans.