I get the rules state that, but they introduced the yellow card sanction for a reason.
I'd say the wording of it refers to what I mentioned earlier, you take out a player on purpose - red card. The wording even implies this with acts to prevent the goal on purpose e.g. pulling shirt.
Luiz is essentially kicked, it isn't a trip because of how far away he is. The striker has taken a. Massive swing, so in a running situation he is nowhere near him for a 'cheeky trip' like some of you mentioned.
So the argument is... We've introduced the new law to prevent double jepeordy, this isn't really matching the law, but we haven to categorise it as something, let's look at the law and reasoning behind the whole law change... has Luiz done it to take out the player? No so caution.
Clatternburg, arguably our best referee for decades has said it should have been a yellow. He said that's accidents like that are deemed as a caution.
BBC are quoting it should have been a yellow with some rules they've found? Although the text isn't from the actual rule book
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The United one was worse because it was a massive dive from Martial. Both utterly ridiculous and lack of common sense.