Even though this appears to be a filler chapter, it is not. 30 chapters later, you will go back and see this is the starting point of several plots.
This is a flashback chapter, and it occurred after chapter 42. In the LN, the people rescued by Eris here has already met Eris and Rudi again before chapter 45, firmly establishing them as repeating characters, thus important plot line characters. Logically, that meeting scene can only be introduced after the scene showing Eris rescue them, but there is no way for the reunion scene to be shown to establish the importance of the those people.
Mushoku Tensei is known for subverting troupes, and soon things seen in this chapter will be subverted. So just watch for the jaw drops next chapter.