Yep, think it was just the cameras that identified it. According to this Ferdinand didn't hear him.
From The Guardian at the time .....
The incident
What we know The next image of the footage is the key clip of a smiling Terry shouting something back towards the QPR goal, with the defender briefly obscured as Cole walks across the camera shot. It is hard to judge how close Cole is in reality to Terry at this exact moment. Once the left-back is out of shot, Terry appears to mouth the alleged offensive comments before the camera cuts to jubilant looking QPR supporters.
John Terry's view Terry's camp have suggested that the centre-half only became aware that Ferdinand believed he had been the subject of racial abuse when Cole shouted to the England captain as he retreated towards the halfway line following the concession of the free‑kick. His response was to shout back towards Ferdinand that he had never said the offensive comments.
Anton Ferdinand's view Ferdinand has not spoken publicly on the matter, but figures close to the centre-half have suggested he may have had no idea Terry had used racist language in the incident.
The dressing room
What we know Terry sought out Ferdinand after the game had concluded, with the QPR player visiting the away dressing room where the England captain sought confirmation that Ferdinand accepted his version of events.
John Terry's view "Anton and I spoke for 10 minutes in the dressing room after the game and there is no issue between us," Terry said. Cole was among the players also in attendance and the conversation was witnessed in part by the Chelsea manager, André Villas-Boas, as he headed out to conduct his post-match media duties. The pair ended their chat by "high-fiving and embracing" with the situation apparently resolved.
Anton Ferdinand's view He claims that Terry approached him after the game, asking: "Are we cool?" Ferdinand said they were, which may have been because the QPR defender had had no idea there had been an issue between them in the first place.