> Participating subjects were shown a selection of cards, each of which had a letter on one side and a number on the other.
You skipped that part just above your quote. There is no ambiguity. In both this experiment and the original experiment they were given that information before their selection.
beyondCritics was attempting to be pedantic, and failing due to not reading, that the problem in this linked article was not presented with the context that the cards were always letter/number pairs and never letter/letter pairs (in which case you'd need to check the K card). Just a few sentences earlier in the article from what they quoted, though, it presents what I quoted, that the cards are letter/number pairs.
To support my claim though:
From the experiment in the linked article:
> Four cards are placed on a table in front of you. Each card has a letter on one side and a number on the other.
That statement is included in the text provided to participants.
From the original experiment:
> The subjects were told that cards with letters on their front had numbers on their back and vice versa.
Subjects were tested only after being given this information. Satisfied?
You skipped that part just above your quote. There is no ambiguity. In both this experiment and the original experiment they were given that information before their selection.