Why was kennedy careful to call what the navy was doing a quarantine instead of a blockade?

it was called a blockade because by international war a blockade is an act of war. Blockade would have stopped anything from going to Cuba, which means a threat of starvation would happen in Cuban cities. The wouldnt have been a good idea and could have lead to a full fledged war but a quarentine on the other hand limited restrictions to offensive weaponry which the rest of the world was reasonable to. By going with the term quarentine the U.S. was able to remove Cuba of their weapons against the U.S. To the world's eyes JFK chose to make a fair choice.

the indians crossed artificial boundaries, setting the stage for conflict