The point of the excerpts are that at one time he was highly involved in the communist party, although not specifically the Soviet Union and it would seem that would be the time he was supposed to be ruining America. His most memorable work all appears to be from before his membership even and then before the time mentioned in the book you have cited.
As for the art, I don’t get much out of anyones I have seen so I am probably not the one to ask. People can get meaning from those I’m quite sure. I just don’t buy that there always has to be one acceptable meaning from the creator for any piece of art.
Have you ever heard of the popular front? Look it up.
"as Utley's book suggests, it was precisely Picasso's unique position—that he was so popular in the West and rarely doctrinaire in his own work—that gave him such a powerful role in the cultural dimension of the Cold War. "Thorez realized this best," Utley says. "Let him alone, he serves us best when he is seen in Europe and America as happy among us, and paints as a man." ...
How naive you are. Of course he couldn't ruin America on his own. He was part of a much larger movement to degrade our culture and propagandize for the communists. Again, see "Popular Front".
"The Popular Front sought to enlist Western artists and intellectuals, some of them not party members but “fellow travelers,” to use art, literature, and music to insinuate the Marxist worldview into the broader culture. The murals of Diego Rivera, the poetry of Langston Hughes, the novels of Howard Fast—all exemplified this approach. It’s an irony that communists should seek to change the culture, of course, since Marxism holds that culture is merely a reflection of underlying economic structures, whose transformation will bring about capitalism’s inevitable collapse."
http://www.city-journal.org/html/15_3_urbanities-communist.html