Hello Dragonfly. To be honest I don't really know. I do know that for many years people with a mental illness who have a creative side to them have been said to have been touched by fire.
Although it has often came to mean someone with bipolar because of Kay Redfield Jamison's book Touched with Fire: Manic-Depressive Illness and the Artistic Temperament. However the term originated long before that and certainly can be attributed to any mental illness.
In the case of the art show Touched by Fire, it was started by John Burghardt whose daughter had the potential to be a brilliant artist and who suffered from bipolar.
John talks about his daughter and at one point says " Gradually, the demons in her life overcame the happy times and the creative moments. In July 2005, Rebecca chose to end the battle by taking her own life. see
http://www.touchedbyfire.co/1607-2/ I have often heard of demons of hell touching those of us with a mental illness. Is this how the term touched with fire got started? I don't know, I can find no specific reference to it.
For more about John's and Rebecca's story, please also see
http://mymentalhealthmap.com/MDAO/Stories.aspx#Story_2 Take Care. paul m p.s if you click on the last link and then scroll down the page some you will find an interesting guy LOL.