The common narrative in the world was that of the US disarmament of South Korea. Due to fears that South Korea was going to strike first, the US military recalled many South Korean weapons. Taking advantage of the sudden superiority in both man and firepower, the North Koreans invaded South Korea.

Firstly I'd just like to say that there was no coherent "Communist World" and that "Communism" manifested itself in vastly different ways in different countries. The idea of a monolithic "Communist World" is a relic of the Cold War. However, if we must accept the term, the main narrative taught throughout the Communist world was that of one country or organization meddling in another country's affairs. North Korea, before the war and at the beginning, was more developed and prosperous than the South, which would have been crushed were it not for US/NATO force intervention. The Communist World was therefore more focused on the US/NATO's attempts to intervene in a civil war for the sole sake of isolating communism. They saw a brutal dictatorship in the south crushed by Communist forces, only to be restored to power by a series of foreign powers. The Chinese invasion of North Korea "rebalanced" the war in favor of the North Koreans who had, prior to American/UN intervention, already basically conquered the South.

TL;DR "Western powers supporting any side but the Communist side when they should not have interfered in Korea's domestic conflict" was the narrative held by many in the Communist World.

source: https://www.youtube.com/watch?v=iIobfyaiAUU (The Korean War in Color)

source: On China by Kissinger