Those were flashbacks, I believe so
As RD said it's flashbacks. There are three moments in the story : 1-the present (the war, the duchess and the fucking glassed bastard) ; 2- the retorn of Taki in his country with Klaus (the presents chapters) in wich, maybe, the author will explain the reason why Klaus is now so cruel and angry with his lover and why Taki seems to reject Klaus' love; 3- the time when Taki was in school and his meeting with Klaus and the beginning of their love.
Wtf were the chapter not in order? It was hard to fallow the plot because of it and hard to understand what was going on! Ugh I'm mad but overall I really liked it! Klaus and taki make a good couple!!!! ٩(๑❛ᴗ❛๑)۶ (ノ≧∇≦)ノ Yeah !!!!!!!!!