How did they do that? The deepest well we ever drilled in the history of the world does not even gd deep enough to get 10% close to the center.
The article makes it clear that there is no need to dig down near the core. The antineutrinos pass through everything.
Neutrinos aren't much interested in 10% or 90% or 100% solid lead. If physics, especially particle physics were easy to do it then everyone would and you could be a pundit.