A playing card is a hand-sized piece of heavy paper or thin plastic. A complete set of cards, such as the Guardians, is a deck, which is also known as playing cards.
Is theory11 making a new deck of cards, or will theory11 make a new deck of cards -- I do not know. However, the use of diction with "Playing Cards" does not, necessarily, mean that theory11 is.
Cheers,
JTM