Your screen shows you got keefer's first cast of the tourney, Sketch's was 1st cast ever on that toon, that's the diff. Don't worry, you are clearly missing the point.
I thought I could top that with the sea turtle in 6 casts but it seems getting a keefers has a way lower chance according to wowhead, like 0,02/0,03% while sea turtle has like 0,2/0,3%.
But then again, I also got 3 keefers once in 1 tourney, weird rng these fishes have.