I believe he is offside - but since he is not interfering with the goalkeeper - indeed is in fact several yards away with his back to the ball - then he is not committing an offence. I don't think this is a new rule - he didn't touch the ball.
As for being in the 'keeper's line of sight - there are two Hearts' players definitely obstructing his line of sight, so even if the Celtic player wasn't there, 'keeper still wouldn't be able to see anything.
Have you got another still about two seconds later...