Not quite sure how to answer the first question having never seen the video in question but I can do the second one.
In the years after WW2, late 1940s and ‘50s, the film industry was targeted in suspicion of promoting communist propaganda. The House Un-American Activities Committee (HUAC) began investigating Hollywood and subpoenaed workers in the industry to appear before them and renounce communism. Those who refused to cooperate faced the threat of imprisonment and being put on a black list. This blacklist was a list of people with suspected ties/sympathies towards communism who the Hollywood industry had chosen to shun. Once placed on the list, it was impossible to be employed in the industry.