You win in blackjack when your hand has a higher value than the dealer's hand, but doesn't exceed 21. You also win if you stay under 22 and the dealer gets more than 21.
If a player's first two cards are an ace and a card with a value of 10 (such as a 10, Jack, Queen, or King), this is called a "blackjack" and it is the highest hand in the game. So, in the context of the game, a blackjack does beat a hand with a value of 21 that is not a blackjack. That doesn't occur.