For the briefest of moments, George truly thought that Jim was going to just blow him off and keep walking. He wouldn't have blamed him if he had. It wasn't as though the teen knew him, or had any reason to believe what he was saying was true. Hell, if he'd gone through half of what he was starting to realize Jim had gone through while growing up, he likely wouldn't have believed it either. But it was the truth and George stood on that fact alone, waiting for a reaction from his son and trying to prepare himself for the worst while hoping for something else.
When Jim spoke and George realized it was going to be the something else, that he was going to get a chance to talk to the teen rather than having delivered a monologue that was ignored, he felt the beginnings of relief wash over him. He was still upset with the teen for what he'd said to Winona but George was the adult in this situation and he could act accordingly. Besides, he figured that a conversation that carefully avoided rebuking was better than no conversation at all.
"I think," he replied in that same easy-going tone as before, "that you're used to people being irrationally angry with you and decided at some point between driving my car over that cliff and the age you are now that it would make more sense to give them a reason to be angry than keep getting in trouble when you were doing your best." He'd deliberately mentioned his car in passing just to make it known that he knew about it and certainly wasn't going to rant and rave and rage over its fate.