"While a "spiral" and a "helix" are distinct as technical terms, a helix is sometimes described as a spiral in non-technical usage." - http://en.wikipedia.org/wiki/Spiral
They are different, but people who don't know the difference often call hexixes spirals, as is the case with spiral staircases.
I'm fairly certain that the non-technical sense by far predates the more narrow technical definition. It's all about context, and there was nothing here that would make helix more correct than spiral.
They are different, but people who don't know the difference often call hexixes spirals, as is the case with spiral staircases.