If I was to guess.
It's sick/injured and needs assistance eating in a tank full of other fish that would snatch the food away.
A demonstration of a very well trained/calm fish that can be held and hand fed.
Hippo tangs are weird Yo, and maybe it likes it.
Side note, I know they get big, but I rarely see specimens with something to compare their size to, and this one still has a ways to go. Beauty fish.