When compared to the screencap below, you notice he doesn't have the sideburns and the bottoms are different. I think the above pic is just a candid photo of Heath around the set. He is in his own clothes! 
Actually...my guess, after extensive watching of the movie and studying this photo...this was an outfit he was going to wear in the sex scene with Alma right before the divorce ("I'll have 'em if you support 'em" scene). What we see is them both nude in bed. Perhaps there was something leading up to that that we didn't see? Notice the sideburns in this shot, plus he is wearing a wedding ring. The set definitely looks like the Riverton apt.
Look at Heath's feet, doesn't he look like he's jumping off the ground? You can see shadows under both shoes.
