makeWebRequest returns responseCode -403 although traffic log shows 200

I'm making a web request and the weird thing is that I get a different responseCode in my code than in the traffic log.

I make a simple request like following:

function makeWebRequest(url, params, callback) {
	var options = {
		:method => Communications.HTTP_REQUEST_METHOD_GET,
		:headers => {
			"Content-Type" => Communications.REQUEST_CONTENT_TYPE_URL_ENCODED
		},
		:responseType => Communications.HTTP_RESPONSE_CONTENT_TYPE_JSON
	};
	Communications.makeWebRequest(url, params, options, callback);
}

function loadWeatherPreview(callback) {
	BackgroundUtil.makeWebRequest(
		"https://api.openweathermap.org/data/2.5/forecast",
		{
			"lat" => Props.get(Constants.PROP_LAST_LOC_LAT),
			"lon" => Props.get(Constants.PROP_LAST_LOC_LONG),
			"appid" => Props.get(Props.OWM_KEY),
			"cnt" => 7,
			"units" => "metric" // Celcius
		},
		callback
	);
}

In my callback I get -403 as result code and an empty data value, but as you can see in the screenshot, the traffic log shows that I get result code 200.

How can this be?