Mc has been on what's his faces jade boat before, and the guy just rode up on it. Being that it's the only one that mc's ever seen(as far as has been shown), wouldn't he be able to put the pieces together? He had to be shown blatantly before he realized, so sad. I'm honestly surprised the guy bothered to reveal himself at all.
This whole competition was confusing, but I guess it was as good an excuse as any to spark rivalry and induce hatred into the "main plot".