It's true.
Chinese algea eaters, if it's the same species that I think you mean (I don't know any common names) will start out eating algea, but then turn into a predator sometimes later on.
IME, most algea eaters will turn and go after other fish at night when they are more active and the fish aren't as active, if they don't have enough to eat.
That's why I always suggest a diet of zuchinni, cucumbers and spirulina discs for them no matter how much algea is in the tank. Sometimes they won't even touch the algea at all.