It would certainly be unusual for just one wing to moult as birds normally moult & re-grow both wings together - but only 1 or 2 feathers on each wing at a time. If several feathers are missing on one side, I would think that he is being picked on & those feathers were pulled out by another bird. I'm glad you moved him to his own cage. If the feathers were pulled out, they should re-grow - but it will take a bit longer than if they moulted on their own. If the feathers are broken off, it will take even loger as the base will have to moult before the new feather will start to grow - similar to clipped wing feathers.