As far as the chapters go, some times things can be changed around between the serialized version and the collected version. Bino mentioned how she moved later chapters into volume 1 of JoshiMuda just to have most of the characters introduced by the end for instance. My guess is that Ojiro probably came up with this chapter for the tankobon deciding that it flows better with something bridging the serialized versions of chapters 3 and 4 and then setting up the a future plot point -- the trip -- as well.