If you look on the 1:25,000 os map it *is marked as a standing stone. Not that that's 'proof'. And it's listed on Coflein
http://www.coflein.gov.uk/pls/portal/coflein.details_test?inumlink=6000619
Though they're not giving any date.

It could be a cross shaft, but in the photos it's not a consistent cross section, it looks a bit wibbly - if that means anything.