A bit wider context. It's about a supermax prison.
One says: Prisoners could escape that way.
The other one replies: From what we've been told about this supermax prison I think there's no way that escape is that serious of an issue. Every prisoner is kept segregated, and then shackled and searched when they need to take a
No, since you have now included the word 'supermax'. The phrase means that probably any escape is too difficult. The seriousness is that of the prisoners, not the guards. There is no reason to think seriously about escaping because escape is impossible.
I think they are saying the tunnel isn't going to lead the prisoners far away from the prison and they probably have the other end guarded. That's why they don't seem concerned.