I tested with a US location (San Francisco) and it seems to be also returning in Celsius.
One would assume that the US would be in Fahrenheit.
I would expect it to always give the same unit. What if someone from France wanted to get weather for New York? What if someone from St Louis wanted to get the weather in Tokyo?
You can’t just assume that location will dictate what units they want - what if someone from Peru is on vacation in San Francisco?
So if you design an API like this, you have to make a choice. You can choose a set of units to use, and hopefully explain it in the documentation and let the requester convert it however they want Or, you can have the user tell you what units you want and you convert it for them.
To me, the first option is easiest. And the metric system is standard for most of the world so that would be the way to go.