I'm not arguing about NO's judgement of when he does or does not issue cards. As I said earlier, if he didn't believe a card was necessary, he could simply have had a word on the run with the tackler to be careful with his technique and no-one would have batted an eyelid. However, to make the statement, "I'm not going to give you a YC because a try was scored", is basically telling the infringing player, "You have just committed a YC offence but I'm going to let you get away with it this time".
The bottom line is that the offence either deserved a YC or it didn't. The fact that a try was scored immediately following the offence should make no difference.
I like NO, I think he is probably the best in the business when he has a good day and is still in the top three even when he has a bad day so my comments are not a personal attack on NO. In the incident we are discussing here, I believe his choice of words were poor.