Mythologies

The other day on NPR, Chris Rainier, a reporter for National Geographic, was talking about the Tsunami. I didn't catch which country he was in, but he said that this people's "mythology" told them to run if they noticed such severe weather/environmental changes. Many of these people subsequently survived; their "mythology" had served them well.

I believe he was talking about the religion of these people. Now, why is it considered okay for him to call it "mythology"? I still don't understand why we call ancient Greek religion "mythology". What makes one thing a religion and another thing a mythology? Certainly, the disbelief of the speaker - it isn't his/her own religion. Also, the belief system in question is not a part of the culture of the speaker's own country. What else?