OpenWeatherMap has that same default location issue sometimes. I had better luck with WeatherAPI.com for my projects. Their free tier gives you current weather and a forecast without those weird defaults. Just make sure you handle the API key correctly in your code.
Yeah, that default location trap is so annoying. I ran into the same thing with OpenWeatherMap a while back. I switched to WeatherAPI.com and their free tier has been solid for basic current and forecast data. Just remember to add some simple error checking in your code for when the zip code lookup fails, so it tells the user instead of guessing.