I actually think that the answer is incorrect.
I believe that you need to flip over all of the cards to ensure if the rule is false.
Consider the following scenario:
A -> 3
K -> 3
3 -> A
7 -> ?

Now, the article says that "most people get it wrong is that they mistakenly assume “3” has a restriction placed on it. That’s not true though since only “A” must say “3” not the other way around." but, when you turn the card over, it does have the restriction !!!