They are very personable fish, and each one is different. It is not uncommon for a flowerhorn of any size or age to act differently in a new environment.
The longer he is in his new enviroment the more he'll settle in, try not to change it up. Also the more you interact with him, the more he'll recognize you and interact with you. I've had flowerhorns with instant personality following me and ones that have taken months to warm up to me. In the end they are all like water puppies in their own unique way. I breed, import, and have my pet flowerhorns, one of my pet flowerhorns I imported from Thailand and he was absolutely crazy right out of the box. Another one of my personal pet flowerhorns is so laid back I can have him in a tank with anything and he could care less. He is still a great fish, he took like two months to warm up to me. He's actually my favorite as he swims right up to the tank to see me because he likes it when I pet him and hand feed him treats. Anyway your fish is a great looking flowerhorn and he will come around.