I believe playing cards in Food Court can be considered as not acceptable because :

1) The intent of the space designated as Food Court is eating food. Playing cards does not suit there.

2) By Playing Cards in the Food Court, they are denying the opportunity to other users to use the space for the intent that it was suppose to serve i.e. eat food.

Having said that, a more dilligent approach from the Manager would have been to ask them politely to stop playing cards rather than snatching away the deck, but then...