Meh, they could have picked basically any chemical element or molecule to base their freezing/melting/boiling temperatures around. In the case of Celsius, they chose water, H2O, at sea level, at Earth’s atmospheric pressure, to base their standard temperatures around.

A hypothetical standard temperature scale could just as well be made around iron in a vacuum with zero atmospheric pressure floating around in space with zero gravity, but that’s not very practical down here on Earth, and water is rather abundant on the planet (ok let’s not get into the whole pure vs saltwater thing, but you get my point).

Anyways, both Celsius and Fahrenheit are equally scientifically valid, as there’s a direct conversion formula to go from one to the other. Fahrenheit just seems easier to us in the states when thinking about the weather. 0 is fucking cold, 100 is fucking hot.