Why are Japanese a quite quiet?

Last week, my class was absorbed into other class due to a shortage of students.
There are many strong students who came from France, Israel, Spain, and so on.
I always talk to them with the full extent of power to catch up with their quick talking; otherwise, I would be quiet.
There are also some Japanese students in the classroom. One day, I listened to the conversation of an Italian a French and a Japanese during the brake time.

Japanese: Hi. How are you today?
Italian : Yeah. I'm fine. I went shopping after school yesterday and...(5min)
...But I think that's...(3min)...And you?
Japanese: Ah, well, yeah, I think so.
French : I don't think so, because...(3min)... Anyway, do you usually...
Italian : Weit. In my country, many people are doing...(2min)...
French : I don't know but...(5min)...

What I realized was the Japanese customs.
Japanese people are normally taught by teacher and parents:
1. You shouldn't interrupt people's talking as it could be offensive.
2. You should start talking after a person has finished.
3. You should carefully listen to a person's talking until the end.

From my point of view, this is why Japanede are so quiet in that they say almost nothing but smile while in a group in class. In fact, it's a bit tough for Japanese, while overseas, to find 'the end' of a person's talking.
But I must change those rules as long as I talk to them.

As a conclusion, I must talk clearly and louder than I used to do in Japan.
And what I think I must more learn is how to quickly gently interrupt.