Paradox!

"Und nun sollten wir alle Teil des "Westens" werden. Neues Geld hatten wir schon - schwere Muenzen und frische Scheine mit "Deutsche Mark" darauf. Manche Menschen hatten auch schon neiue Autos. Jetzt sollten wir neue Ausweise und Paesse bekommen, eine neue Fahne, eine neue Regierung. Das musste gefeiert werden."

This quote reveals both irony and paradox, depending on what viewpoint is taken. If you assume the narrator is seriously and literally saying that such things are truly cause for a celebration, there is the point that not everyone in such a situation would have cause to celebrate. It is impossible that everyone would be rejoicing over such a change (in fact, Olli's father used to be involved with the Party.) Others may have mixed sentiments.
Another irony is that having such thing might not really be something to rejoice over. You will notice nothing like "extended freedom" is mentioned; rather, they are all physical things like a new car.
The point could be made that having to get new passport, a new flag, and new regulations aren't really any reason to celebrate either.
Also, you will notice that the countries aren't "reunited as one;" rather, the East is now just a "piece of the West".