From your own link:

"The speed has a weak dependence on frequency and pressure in ordinary air, deviating slightly from ideal behavior."

"The speed of sound is raised by humidity. The difference between 0% and 100% humidity is about 1.5 m/s at standard pressure and temperature, but the size of the humidity effect increases dramatically with temperature."

"Slight" can matter significantly in an application like this.

> the size of the humidity effect increases dramatically with temperature.

This has little do with the behavior of sound. The fraction of the air that consists of water vapor at 100% relative is very small at cool temperatures and increases to 100% at 100 degrees C.

(Yes, water boils at the temperature at which air that is saturated with water vapor is all water vapor.)