The article is pretty bad. It starts as an anecdote about an inmate beaten to death by the wards, like if it was representative, but then the overwhelming majority of deaths are a result of diseases, overdoses and suicides. Also no reference to the denominator, so you can’t really tell if there is an over mortality in jail vs outside (particularly for the subset of the population that is likely to end up in jail - drug addicts, people with mental problems, etc).