News reports are famous for being selective in the details they include. The artifact in question came from an Elizabethan-era wreck, where its proximity to other navigational gear suggests its use. No actual sunstone has been found with Viking artifacts; the only direct connection is through Norse stories and legends which mention the object and its use.

http://www.cbc.ca/news/technology/story/...ey-crystal.html

http://en.wikipedia.org/wiki/Sunstone_(medieval)