Criminal culture is not, it's something that emerges way more naturally, usually as a direct response to the culture set by police and punishments established by law.
If, for example, the punishment for certain crimes is so high by default that the criminal would rather die than get a sentence that would equal death, then you have taken any and all motivation from that criminal to look for a more reasonable way out, instead preferring to "go out in a blaze of glory" on their own terms.
That's why this whole "tough on crime" approach mostly leads to an escalation on both ends: Cops treat criminals more harshly, criminals respond by acting more harshly themselves because acting more reasonable wouldn't gain them anything anyway so they might as well completely live out their destructive urges.
This is further reinforced through a prison system that's not aimed at rehabilitation, but generally seen as a form of "revenge", as "punishment" and as such victimizes its inmates, which leads to even more resentment, while leaving them utterly unprepared, and with quite a grudge, when they get released back into society.
Which leads to the outcome that it usually won't take long until they get into trouble again [0] because their time in prison taught them nothing except "might makes right" and how sadistic cruelty is a valid way of interaction with other people when you are the one in a position of power.
[0] https://www.prisonlegalnews.org/news/2019/may/3/long-term-re...
Yep. That is what happens in most cases. Which is why I reject the idea that most cops which shoot black people are racist. Sometimes, as is the case of George Floyd, the individual officer is at fault (even if that does not _necessarily_ mean he is racist), however, in the vast majority of police shootings, the victim is trying to reach for the cop's gun, assaulting the officer, or in some other way is putting the officer's life in danger. So you can not blame the individual shooter in such cases.
You can, however, blame the systems which cause the erratic behavior, that's true. However, we need to have an honest conversation about what the causes actually are.
The gang culture in prisons is indeed a problem, but making prisons less tough would not solve this problem - it would only exacerbated, as gangs would have increased influence over the prison. Of course, in reality many gangs are in cahoots with the prison staff, which is a corruption problem which needs to be solved.
Another problem the article correctly points is non-violent offenders becoming violent as a result of their time in the prisons.
That said, the gang culture in prisons is only an extension of the gang culture outside of prisons. And you can not blame that on tough sentencing, as the gang culture exists in many other places around the world - in the UK grooming gangs, in Sweden's no-go zones, in Romania's gypsy gangs and so on, all countries without harsh sentencing.