Judging by their deeds, however...
The guys who were captured in Korea were "brainwashed" in North Korean POW camps. Their ideas were formed in the stressful context of war and long imprisonment, as referenced in the article.
Jihad Johnny came to his sincere views, voluntarily, in the free and open environment of Marin County, California. Later, his volutary schooling in Yemen. Then Pakistan. Then Afghanistan. Then he voluntarily went to support the fight in Kashmir. Then took up arms in Afghanistan. He was something like a POW in Mazar-i-Sharif for about a week, then U.S. custody.
He freely and sincerely took up his views before the imprisonment. The story about the Korean War prisoners is interesting, but a red herring as to understanding Jihad Johnny.
...
If there is any brainwashing going on now, its from his lawyers and family trying to get him to renounce his heart-felt beliefs. THEY are the brainwashers. ;)