My definition of event . The choice is the event.

I understand what the example is trying to get across they just explained it poorly. .

They are trying to explain the principle behind card counting, which is to know what cards are left in the pack and that for each event we have to recalculate the odds to better the chances of choosing correctly over many choices.

Th difference is blackjack has an element of randomness, the dealer does not know which card will come up.

Monty Hall knows which door has the car.