It appears that this web service has a rather obvious defect, the Content-Type is set to "text/html; charset=utf-8" yet, the response body seems to be JSON rather than HTML. The proper Content-Type should be "application/json" with Content-Disposition to "inline". Perhaps they didn't do this since some browsers ignore the Content-Disposition with this Content-Type, and prompt to download the content regardless.

Even so, "text/html" is still wrong. Since the content actually isn't intended for a JSON parser, but, a human, "text/plain" would be the most conservative (and not wrong).