The 10m figure corresponds with the other info in the article. The posted article says that the tunnel is used in place of the 7km (4.3 miles) trek around the mountain. That wouldn’t make sense if the tunnel was 8 miles long. Also, I cannot imagine one man could haul away and find a place for all that rock in one lifetime if it were 8 miles long.
I assume that "10m-long, 4m-wide" should be "10 km long, 4m wide." Ten kilometers is not eight miles, but it's not too far off.