The point was an observation that Wallsend is not the only end of the wall---117 kilometres or so east is another end. i.e. "Wallsend is the western most end (or one end) of Hadrian's wall" rather than "Wallsend is the end of Hadrian's wall".

It reminds me of when I lived in Victoria, British Columbia here in Canada. The old time locals would always point out that the foot of Dallas Road overlooking the Pacific Ocean was the true "Mile Zero" of the Trans-Canada Highway. St. John's, Newfoundland some 4,990 miles (8,030 kilometres) away claims to be "Mile One". Each one assumes that they are the start of the highway.