Royal Clown Kives (Chitala Blanci) have a zebra/tiger like pattern. It's different from fish to fish, but the distinct pattern formation is usually the same.
Clown Knives (Chital Ornata) can vary in spottings. Some will be spotless to a leopard like pattern (flowers)
More likely, you encountered a Clown Knife. Is the pattern rare? I've seen a few here and there. So I wouldn't say it's rare, but it's not average.
I was just wondering because there is a approx 15 inch one here in SW Arizona that needs rescueing really bad. I can't take him but I was hoping maybe that would make him more appealing possibly and raise his chances.