Perhaps the "flowerhorn *or* betta" is the result of an ESL speaker and it should have been "flowerhorn *on* betta".
That fish is definitely a betta not a flowerhorn. I hope it is not the begining of a breeding program to develop "flowerhorn bettas".
I would certainly adopt that fellow, and his hump doesn't seem to be causing him problems at the moment. However, I worry about his future. I know that ranchu goldfish, which are grown for their headgrowths, do sometimes need surgery to remove excess growth from obstructing their eyes, etc. I the hump stays the size it is he may live a long and healthy life. If the hump keep growing, there may be serious health problems down the road.
To sell him as a "flowerhorn" when he is a betta is inviting some half-knowledgable fish owner to give him the wrong care and living conditions.