The response is gzip'd. You can see it in the response headers:
So, you need to unzip it. You can do this either changing your whole approach and using cURL, or using the stream wrapper
compress.zlib://. Just prepend that to the URL:
That will get you the correct response. Notice that this is still a JSONP response, so it's in form of a callback. You need to decide what to do with it.