Child greeting the mother’s return

I don't understand what "greeting" means in the following context. "Greeting" usually means saying hello to others. But in the following context the mother has not yet returned, so how the child is greeting her return? Does it mean "the child seeks the mother's return"?

Context:

Freud witnesses his one-and-a-half-year-old grandson throwing a cotton reel in and out of his cot. The infant makes the sounds ‘o-o-o-o’ as the reel is thrown out, its return accompanied by the sound ‘da’, which Freud, along with his daughter, interprets as the German ‘fort’ meaning gone, ‘da’ meaning here. Freud reads this game as a symbolisation of being able to control the mother’s disappearance and appearance so that, rather than waiting and being dependent on her, the infant is now able to represent her absence to himself, exchanging ‘the passivity of the experience’ for ‘the activity of the game’, which for Freud signifies a sense of mastery even as it points to the remembered unpleasurable event... Even Freud points to the double-edged nature of this scenario. In an intriguing footnote in ‘Beyond the Pleasure Principle’, he describes the child greeting the mother’s return with the words ‘bebi o-o-o-o!’, saying that in his solitude the child has ‘found a method of making himself disappear. He has discovered his reflection in a full-length mirror which did not quite reach the ground, so that by crouching down he could make his mirror image “gone”.’ This is a much less masterful solution to the pain of loss, whereby the child acts it out by using his own image as a ‘surrogate’ object for himself.