“The work to make the escape route was done from the outside. This was a break-IN, not a break-out.”
The article says it absolutely could not have been done from the outside. The manhole cover, the exit point where any outside tunnelers would have had to start, was opened from the inside.
The article is wrong.
One block below where the manhole cover is located is the prison power plant. Look at the map of Dannemora. There are tunnels that run between the power plant and the prison. Underground in the prison is like a rabbit warren with steam, sewer pipes and wiring.
All the noisy drilling and cutting was done outside the prisoners’ cells before that night.