That Rainbow is a hatchery fish so the short answer to your question is they are generally not cannibalistic. With that said, once they've been in the wild for months, and in the absence of other recognizable food, they'll eat anything and the bigger ones are more likely to target the smaller ones when food gets tight. They generally aren't predatory on their own species (like bass), but once they figure out that there's no more Purina Trout Chow coming, they'll eat anything. I am surprised they didn't strike on your other jigs.
I used to work at a fish hatchery, rainbows were easy, kind of like the cattle of fish husbandry. We also raised cutthroats, steelhead (ocean going Rainbows), and Silver salmon. They would eat any of their siblings if they were smaller or were facing them. Lots of times I'd see a fish swimming around with another fish hanging out his face because it was too big to choke down. Didn't prevent them from trying though.