As Chlidonias said, this is A.pyroferus and it's mimicking Centropyge vroliki. However, it is just starting to change.
There is no confirmed reason why they mimic dwarf angelfishes, but the most widely held view is that the Dwarf Angelfishes in the Centropyge are very wary and remain close to shelter, thereby being a harder meal to catch for predatory fishes. Predators are unlikely to waste energy attempting to catch a small prey that has a high chance of escape.
