About speaking Japanese and singing Japanese songs

I saw NHK TV program on my Japanese class yesterday evening. It was a singing contest. Some contesters behaved formal, but didn't get high score. Some behaved out going, and they got high score. Those who sang well usually couldn't speak Japanese fluently. Those who spoke Japanese fluently usually sang not well. It's very interesting.
I am not good at speaking Japanese nor singing Japanese songs. My classmates told me the Japanese judges judged by their country's standard. I think he was right. In fact, most of contesters did very well.