Hornworms eat on the leaves of solanaceae family, which have a deadly toxin, solanine, in their leaves. Nightshade, a famous deadly poison, comes from a plant in this family that has a tiny, black fruit. What is amazing is that some of our most-eaten and favorite foods come from this family (potatoes, tomatoes, peppers, eggplants). We never eat the leaves, but the fruit or tubers that we do eat are free from the poison.
As the hornworms eat, they take in the toxins, which protects them (when they can be found) from birds and other predators. I tried feeding them to my chickens when I lived on some acreage, but they usually would take a peck at them and leave them alone. I would not chance feeding them to your fish, because it would have a good chance of killing them.
What you saw in the video were perhaps not feeding on solanaceae leaves, or maybe species with less of the solanine toxin in their leaves. I would still not risk it.
Thus seeking corroboration. 
