That's not what s/he said. The quote is "most cruel justice system in the West, and by quite a margin, too. It is one of a few aspects in which the US is far closer to today's developing and third world countries than to the Western average."

So it says that it is the worst in the west (a term that usually does not include south/central america, even though they are west on a map), and that it is closer to a third world country than many in the west.

From my casual reading that seems pretty much on point.

The justice system does not just mean the prison system, it encompasses laws, police, courts, correctional facilities, some portions of mental health treatment.

If we are bringing up the freedoms enjoyed by citizens in different countries I'd also point out that how the constitution is interpreted seems pretty arbitrary over time depending on who is in the supreme court and what the political climate is. As an example I'm not even sure how solitary confinement can not be considered a "cruel and unusual punishment" under the eighth amendment. I don't get how NSA data collection is not a impacting the "right of the people to be secure in their persons, houses, papers, and effects" of Fourth Amendment. The second amendment seems pretty cut-and-dry in the text that any American should be allowed to have a rocket launcher and that background checks are illegal. I'd hate for that to come true, but if you are following the principle that the constitution supersedes all lower law then it seems logical.

Most western democracies seem to have similar freedoms and similar guarantees that the government will follow similarly given that they are also enshrined in law.

Please correct me if I am wrong, but when I hear americans talk about their freedoms they seem to talk in absolutes, but in practice it's no more free or secure than similar freedoms given by laws in many other western countries.