Why did us officials consider the stalemate in korea to be a successful containment of communism

The temporary division of Korea along the 38th parallel was a success for the policy of containment, as communism did not spread into South Korea. In 1954, SEATO (South East Asian Treaty Organisation) was set up as a copy of NATO. Communism had been prevented in South Korea and the UN was seen as a success.

i'm asking the same thing i asked this other cat all of