No. It is not true. It is true that there is often a talent (especially in the arts) for
many bipolar people. For some it's very strong; for others, it's milder.

Why don't you read Touched With Fire by Dr. Kay Redfield Jamison? That's one of her books that deals with talent in some of the world's best known artists who were bipolar based on anaylsis of their lives. (She is herself a bipolar person with a Phd. in Psychology and is a psychiatrist on tenure at a large hospital in the U.S.)

Creativity usually functions best with an I.Q. of around 120; above that level there is very little correlation between intelligence and creativity, although knowledge may be much broader and deeper at higher IQ levels. An I.Q. of 130 is considered very bright or gifted; I.Q. above 145 is considered genius by some testing standards. I think I.Q.s run the gamut in bipolar illness just as they do in the general population.