I am pretty sure he killed it. The shark was perfectly healthy before that (good color, active, ate plenty). Maybe it was just scavenging but I get the feeling that the gourami killed that fish to eat it. Sounds weird but maybe. I've thought about buying a danio or something else similar in size to the shark (preferably cheap) to use as a test. If it were to turn up dead and ripped apart I'd know.
And yet somehow it seems like cruelty if the gourami takes the bait. Would it be unethical to sacrifice a smaller fish to it just to see what happens?