The article touches on the technical details of this briefly, but the underlying point here is that containers effectively do use the OS, and processes. Like Frazelle says in the article: "a 'container' is just a term people use to describe a combination of Linux namespaces and cgroups." If that's nonsense to you, check out some of her talks, they treat those topics in a friendly way. At the most basic level, though, a container is just a process (or process tree) running in an isolated context.
Sharing library code between processes running in containers is more complicated, since it depends on whether and how you've set up filesystem isolation for those processes, but it's possible to do.
Sharing library code between processes running in containers is more complicated, since it depends on whether and how you've set up filesystem isolation for those processes, but it's possible to do.