Widdershins = turning against the sun = going anti-clockwise = turning to the left = sinister.

It's all part of the ongoing prejudice against left handed people and those who walk their own path.

I'd never heard a specific superstition, but then as 3rd generation left handed (and Limpit makes 4th), we were used to stirring stuff anti-clockwise, turning to the left out of doors and not being able to use tin openers.

LTS