The problem with the modern (latest) interpretation is that the official on the line can see if someone is in an offside position but cannot tell whether that person is interfering with an opponent by moving across or into their line of view, usually the referee has the best view of that. Either way I don't think that Kane could be considered offside under the current interpretations. He didn't actually stop moving though, he wandered towards the route that Son was taking and was probably enough of a distraction to disturb Forster's decsion-making. If you can be bothered to wade through the FIFA spiel then they talk about 'everybody wanting more goals' and so they opt for a more liberal interpretation. I'm all for more goals but not when they are against my side.