Surely some kind of planning permission should have been sought, whether he'd bulldozed it deliberately or not? I don't think anyone would think the henges were just some natural lumps and bumps to bulldoze, anyway. Do you? I mean - seriously. If it were some almost indistinguishable barrow or summat, then maybe. Nah.
Dunno. It all seems rather strange doesn't it. If the land and property were in the hands of an agent during the sale, I wonder if it's possible that a contractor was brought in during the interim period to 'tidy things up a bit' and make the land more presentable? I've not been on the ground there but I believe the section missing is from one fenced off field. Was the view restricted from the other adjoining fields so that the full view of that henge was not visible? Just trying to find a reason why someone should appear to be so vandalous knowing it would cost them dear!