My money is on a big storm cartwheel because it was not tied down well enough.

it does remind me of the guy with a Hobie 18 that though he could tow it home with the mast still up! He hitched it up behind his Dodge Ram and went gunning off towards the overhead lines across the road. The result was both bows snapped off at the front beam [try doing that to a TheMightyHobie18] and no telephones in the neighbourhood for a while!

Paul