They can't have been completely surprised: joining the dots between the known bits of wall made it obvious where it went, more or less. But it's good to narrow that more or less to right here! And there are thigs to be learned, too, about what techniques were deployed where along the Wall.
Yes, it really is called Two Ball Lonnen. Newcastle Libraries explain (but it no longer looks anything like the picture)! This entry cross-posted from Dreamwidth: comments always welcome, at either location.