He's a baby of a different species and speaking a different language
He knows HIS calls and is still learning YOUR calls. He largely is still running on instinct right now. It is abnormal in the wild for him to be left alone, at all, so being left alone is super scary, and then what does any baby want when they are scared? Comforted...and in a lot of species, food = comfort. Do you offer him comfort feedings at all? Some cockatiels don't wean until they are 6 months or older. They all have different needs!