That's very strange, it almost sounds like past data was getting "stuck" in your phone/watch. Were the times on the hourly chart updating throughout the day or were they staying the same? I'm not caching any data on my servers, though it's possible Forecast.io, my weather data service, was doing something along those lines.
Also note that Forecast.io's weather data is very localized, so it might display completely different weather conditions for someone in one part of a city versus someone in another part of the same city. So entering "Shenzhen" into the place search will return the weather for one static spot in the center of the city, whereas if you're using your current location then it'll return the weather for your exact location in the city - which could be miles away from the city center.