I don't know how his breeding set ups are, but I think the quality of care the birds receive matters much more than the quantity of birds raised. It seems like he raises mostly breeding birds and babies that are to be handfed go to different professional handfeeders where they can get more individual attention. Breeding birds who are not tame are usually quite content to live in an aviary with a mate with no human attention beyond basic care, so I wouldn't really consider it a mill if the birds receive proper care -good diet, large cage/aviary, enrichment (toys or fresh branches to shred), proper vet care), and are not overbred. He seems very knowledgable about the species he raises. Usually the larger breeders like that also do provide good vet care, a disease is more risky, and it's more economical for them to provide vet care as well, as they can afford to just have a vet come to them to check their birds rather than trying to pack up untame birds to bring them to the vet.
Of course some people would object to him selling unweaned babies to professional handfeeders. Some object to breeding for pets or handfeeding altogether, and others feel that a breeder should sell only to the pet owner so they can get a feel for the home that would be provided. I do think that that is important. All the same, I see people on this board who handfeed and raise babies that they get unweaned from breeders like this, and they clearly do care about giving them the best possible start and finding them good homes.
Now, there are places that are true bird mills. Breeding birds in small cages crowded into trailers, often without proper perches. I was at a flea market once where one vendor had birds and I feel the breeder must have been a bird mill. They were selling budgies and lovebirds by the pair - already stuffed into ridiculously tiny cages. They had about a dozen sun conures - all undersized - all stuffed into one cage with one dowel perch, seed, and water. In another cage, they had a baby blue and gold, an amazon, and a few eclectus. Those birds all looked like unweaned babies, one eclectus appeared unable to perch yet (not unhealthy, just young - I hoped). No toys, a bare minimum of dowel perches, tiny cages. THAT is a bad breeder - with stunted birds, selling unweaned birds to the public.
EDIT - Well I want to change that. He may indeed qualify as a bird mill if the pairs are in 3x4 cages and eggs are removed as they are laid. I had no knowledge of his particular set ups. Still there are some larger breeders - not as that large though - that do provide pairs with proper flight aviaries and enrichment and ensure that babies get enough attention. But Voren's set ups do look pretty sad.