When I had to separate one of my bantams recently she didn't want to eat because she was nervous in her new surroundings in the house. Took her a day to start eating. I would dip his beak in water several times a day to be sure he is getting enough water. Some chickens don't like the taste of the ACV, so I would leave it out and put vitamin/probiotic powder in his water with a little sugar. I like the Rooster Booster brand that I buy at Tractor Supply. My chickens prefer "scrambled" egg and LOVE Quaker Old Fashioned oats dry. I would try different foods to see what he likes best.
Good luck! He sounds SO sweet! I love my Silkie roosters best. They have loads of personality!