No, it is him.
We can compare the two men's height's against one another in the photograph. Lightoller was 5'10 whereas Pitman was 5'8. That's exactly what they look like in that picture.
Lightoller's appearance underwent some change after the Titanic disaster.
Head over to Dan Parkes website and look at the photograph collection he has of Lightoller.
Titanic's Officers - RMS Titanic - Second Officer C.H.Lightoller
Look at the photograph of Lightoller taken aboard the Oceanic several months after April 1912. It is clearly apparent that the disaster aged Lightoller at least five years and left him with a very worn, gritty face, he also looks to have lost weight.
Look too at his 1919 merchant navy ID photograph. The combination of the Titanic disaster and multiple stressful wartime experiences left Charles Lightoller looking much older than he was.