[Disclaimer: the following is part generalisation and partly reflects my personal experience of the French education model, so please don't flame me; France is a big place and the teaching obviously varies from place to place!]
I think French society in general is outwardly more formal and polite than the UK nowadays and schools reflect that cultural difference. Also there is culturally a greater emphasis on personal responsibility. This is a generalisation but French women in particular tend to be quite tough and there is a certain pride in French society on looking after yourself and taking life seriously.
Brits make the mistake of characterising French people as being relaxed and full of "joie de vivre" and they can be during their long holidays, but most of the time they are fairly conservative and rigid about following rules and paying attention to details. And they are a more traditional and insular society than the UK I would say.
The French school curriculum is quite old fashioned and rigid. There is a lot of learning by rote. And the way they treat pupils is quite negative I would say. No one gets marks for turning up and washing their hands or a prize for taking part! You have to earn your marks and as a student you get compared to a model of a "perfect" pupil and get marked down and criticised quite harshly if you don't fit in to that rigid model of academic perfection (although there are opportunities to follow a less academic route early on in secondary school).
Schools are there to provide an education, there isn't a lot of pastoral care, and if you as a pupil choose not to take advantage of the teaching on offer, then tough luck. I think that parents and teachers are generally stricter in France and the teaching style is certainly more rigid and negative than in the UK. And I agree that there is less misbehaviour in French secondary schools, but my goodness, give French children the opportunity to have some unsupervised down time, say at a party or during a free period, and they absolutely explode as a result of having to be so conformist the rest of the time, whereas British dc would perhaps be slightly more chilled given the same amount of liberty, as they would be more used to it.
Having said all of that, I think overall, French students have a better, more defined balance between work and play, as do their families, as they are forced to work really hard in the relatively short school terms but can chill out or focus on sports or the arts during the long holidays. So maybe their behaviour reflects that difference too?
I am glad you are enjoying your experience there op, hope it continues to be a positive experience for you!