There are a number of ways in which this was the case. Let us look at two of the most important.
First, this conflict involved a direct confrontation with the Soviet Union. The USSR was the main enemy in the Cold War. Therefore, a confrontation with it was more important than one with China when China had only been communist for about a year.
Second, this conflict had more lives at stake. The war in Korea affected the soldiers involved and the Korean people. The Cuban Missile Crisis could have ended up causing nuclear war that would have impacted Cuba, the US, and most likely much of Europe as well.
For these reasons, there was more at stake in the Cuban Missile Crisis, making it a greater test.