Sad but untrue. Yet another aviation urban myth. I doubt that any 707's were fitted with GPWS.
The accident was investigated by the Spanish Accident Investigation Board, who determined the most likely cause to have been pilot error, and a failure to follow proper instrument approach procedures. The pilot was not precisely aware of his position, and the Board determined he had "set out to intercept the ILS on an incorrect track", which placed the aircraft over the wrong terrain for his approach, in a hilly region of rapidly changing terrain height. [3]
The crew also did not respond properly to the ground-proximity warning system (GPWS), which can be heard on the flight recording. (There is a persistent rumor that the pilot responded to the GPWS by saying "Shut up, Gringo" but this is not borne out by the transcript of the recording; the pilot responds to 15 seconds of GPWS warning with "Bueno, beuno", roughly, "Ok, ok" in English.[4][5])
The airport's approach controller was also faulted for providing faulty position information, failing to inform the crew that radar service had been terminated, and failing to maintain proper radar surveillance of the craft.[6]
(wikipedia Avianca 011)