Odette thinks the swamp air is humid because it is hot. Is she right?

No, she is not right. Phoenix is hotter than the swamp, and its air is dry.

At dawn the desert has cooled to 75 degrees Fahrenheit.

Is the desert's air humid now? No: the desert still has almost no water to evaporate.

At dawn the swamp has cooled to 70 degrees Fahrenheit, and fog lies over the water.

Is the swamp's air humid now? Yes: the swamp's water still evaporates, so its air is holding a lot of water vapor.

Fog over the swamp at dawn. The air is cool, and it is humid.

Four readings. Hot is not the same as humid.

So humidity tells you how much water vapor the air is holding, not how hot the air is.