I think this is that fishes' own behavior, which gets reinforced by the owner 'hanging out' right there every time he does it- so basically the owners' proximity, by association, has become sort of a que. Parrotfish lovers always talk about how much their fish seek attention.
The guy didn't dub his voice, because he repeats it too many times. If he'd bothered to fake it, the timing would've been a lot better. That fish just lays down predictably.
;-) funny to see, regardless of why it started.