Also, we do have this image of the very strict japanese high school but we have to keep in mind that these strict high schools depicted in manga and anime are the private ones.
Most of the schools depicted in anime and manga are state schools.
This school setting of this specific manga is probably a co-ed public school — and not saying that’s always the case, but in many many places public schools are just lax with their rules. I doubt that Japan is any different. I have seen some manga depicting such thing (schools that seemed lawless).
Japan is different. School rules in the Japanese education system (especially in state schools, which is most of Japanese schools) are notoriously strict. Dress code, hair code, behaviour, loitering after school hours, sometimes even the type and colour of students' underwear is regulated. Japanese students can get in trouble with teachers if their hair gets a lighter shade over the summer due to sun exposure.
And students who stand out (dyed hair, piercings, tattoos, clothes that are against regulations, being openly gay and so on) are not only liable to get in trouble with the teachers, but are also in many schools practically guaranteed to be relentlessly bullied by other students. Bullying in the Japanese education system is widespread and specifically targets students who dare to stand out from the crowd.
Japan has high rates of depression and suicide amongst its students (high school, college and even primary schools). In fact, during the last half a decade suicide rates amongst Japanese students have continuously gone up. This is partly because students are routinely expected to have high grades (by both their teachers and their families), partly because of bullying, and partly because of oppressively strict school rules and regulations.
I mean, this is something people just should be aware of at least if they find themselves idolizing Japan in some way.
I think this is also a very big reason WHY a some schools in manga are like this one, why anime people have wacky hairstyles/colors, delinquents are a big thing, so many stories have a fantasy/supernatural element and so on and so forth.