I feel like this article is leaving some important bits out for the sake of a narrative.

From Wikipedia

By the early 1940s, U.S. Army Intelligence was already aware of allegations that Qian was a communist

This predates the red scare - at the time the US was in bed with "Uncle Joe" Stalin.

While at Caltech, Qian had secretly attended meetings with J. Robert Oppenheimer's brother Frank Oppenheimer, Jack Parsons, and Frank Malina that were organized by the Russian-born Jewish chemist Sidney Weinbaum and called Professional Unit 122 of the Pasadena Communist Party.[43] Weinbaum's trial commenced on August 30 and both Frank Oppenheimer and Parsons testified against him.[44] Weinbaum was convicted of perjury and sentenced to four years.[45] Qian was taken into custody on September 6, 1950, for questioning [7] and for two weeks was detained at Terminal Island, a low-security United States federal prison near the ports of Los Angeles and Long Beach. According to Theodore von Kármán's autobiography, when Qian refused to testify against his old friend Sidney Weinbaum, the FBI decided to launch an investigation on Qian.[46]

This seems incredibly pertinent to the story as well.