Can you show us a photo of his chest? What about photos of the feathers that came out?
Often when going through a molt it can look like they are plucking the feathers out, but really they are picking out feathers that are hanging on by a thread. They have thousands of feathers and in a big molt they may lose a dozen a day. It looks like a lot for sure!
The biggest thing is that plucking will leave bald spots where molting won't, and plucked feathers will have a bit of material at the base, or looked snipped; a molted feather will look clean.
Babies are not prone to plucking without a medical reason, so my hunch is its molting. If its not molting, a checkup is needed.