They are not really predators, in my experience. I have a 3/4"
in the same tank as the my S. decora, and it's been in there since it escaped through a hole in the breeding net at about half it's current size. And my largest decora is between 6-8" long (total length). Of course, that's the true decora, not a man-made replacement. So it's a bit like saying "rubber behaves this way", and then realizing the rubber is not real rubber, but plastic.
By the way, your fish in the background of picture 2 looks like Tiger Barbs, which isn't a Tetra (Characin family), but an Asian Cyprinid fish (related to Carp). They may well have been terrorising the fins/barbels on the catfish - in India where they come from, there are larger catfish that is definitely "the enemy", so their natural behaviour is to go after fish with barbels and flowing fins, and bite them...
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Mats