The telegraph introduced a means of rapid communication. The proliferation of poles and wires for the telegraph spread across regions like a giant grapevine. This led to the term ‘grapevine telegraph.’ This new term distinguished between the new telegraph system and the old word-of-mouth means of communication. People would utter 'I heard it on the grapevine' to indicate that they received genuine news, instead of unsubstantiated gossip.
That’s where the title of the popular song came from. Now you can listen to the Marvin Gaye version of the song.