could be molting but either way they should grow back in a few weeks. If not there would be a bigger problem! Maybe he just fell in his cage and some feathers got lost. Just keep an eye on it I guess.
y african grey lost a patch of feathers on her head similar to your budgie, this was a good few weeks ago. They are growing back now and Enzo really appreciates me helping remove the tubes for her.
Thanks both of you! I'll watch and see if they grow back, and keep a super close eye on him to make sure he isn't doing anything that could cause him to lose them.