That statement is true, and here's why:
1. Intelligent people can perceive reality in ways an average mind may not, opening up strange new possibilities. If someone came to you claiming to have perfected a matter teleporter, you'd think they were crazy or lying. How do you think Edison felt trying to sell the light bulb?
2. People who score well on IQ tests tend towards autism and other mental disorders. Simply put, their minds perform differently than our own: better in some ways, worse in others.
To me, that is the meaning of the statement "Genius borders insanity".