A small, primitive village has yet to discover fire, which is a good thing because there are highly flammable (but not otherwise dangerous) gasses in the air. The heroes, blissful in their ignorance, don't know that and think it a wonderful idea to show the locals open flame.
Whistling on the sea is bad luck. It is said to mock the sound of a strong wind and will call it so nature can show the true sound. Whistling is only allowed when becalmed or when shrouded in fog.