What was the highest temperature ever recorded on the surface of Earth?
The record the article is referring about seems to be the same as registered at Guiness World Records:


  On 13 September 2012 the World Meteorological Organisation
  disqualified the record for the highest recorded temperature, exactly
  90 years after it had been established at El Azizia, Libya, with a
  measurement of 58°C. The official highest recorded temperature is now
  56.7°C (134°F), which was measured on 10 July 1913 at Greenland Ranch, Death Valley, California, USA.


Those records are usually well researched, and in this case it matches what is reported by the WMO. Since 2007, the WMO Commission for Climatology (CCl) has maintained the Archive of World Weather and Climate Extremes. In that archive, the same record is reported as the current highest temperature ever recorded:



More details about the record are described here.
The official WMO press release about the invalidation of the 1922 El Azizia record can be found here.

It is surprising however, that with most the hottest years on record happening in the last few decades, the maximum recorded temperature is still from 1913.

Some people have questioned the reliability of those old measurements. More recent and much more reliable measurements seem to top-up at about 54.0°C as pointed out by a very interesting article brought up by @Plutor in the comments.

Note that you are mixing temperature and heat index in your question. Make sure you understand the difference.

PS: "Greenland" Ranch... a rather sarcastic name for such a place.



Photograph of old Greenland Ranch Station, California, USA (source)