As everyone notice already this chapter and the following arc were not written by the novel author but by the mangaka artist. It's very cliche and generic.
I think there could be two possible reasons for this. First to reward the mangaka for the good sales of the manga and the second to test how the fandom would react to this cliches specially if they are demanded for an anime adaptation
Well, they got to test out a number of fanservice cliches in one chapter.
Swimsuit chapter
-> onsen
..-> girls' chat
-> tentacle monster and rescue
And some domestic embarrassing situations, like the ojou-sama who can't cook.