White Crane used to state that they didn't contain hormones, yet female African cichlid peacocks would color up like males. lol This was probably 20 yrs or more back now. I would think that Singapore would be far more stringent than Thailand, as far as feed, hormones, or anything else aquatic related. When I was in the tropical feed game years ago our govt here in Canada blocked the importation of most of the Asian producers due to how sketchy they were, some not even allowing govt inspectors to visit. They actually blocked Hikari for 6 months or so when they first cracked down after the melamine in dog food fiasco. (out of China)
But if not hormones, then feed will not influence nuchal hump size, beyond what any normal amount of proper nutrition would aid a male fish in normal sexual maturation. The rest is just Flowerhorn marketing hyperbole. High protein feed for a fish created from fish that are all omnivores, never seemed logical to me, other than most FH keepers focus on fast growth, fast sexual maturation, and aggressiveness which aids both overall coloration, and nuchal hump size. I always raised my FH the same way as the rest of my fish, with longevity in mind.