Also, its supposed to be really dark in the cave, the thing the LN and WN liked to do is contrast the perspectives of characters. So Kumo's perspective is on one end and we see that reflected in the encounter here. I'm not sure if they will show other character perspectives in the manga as characters other than Kumo will be introduced.
On one hand, the side stories had some interesting moments, but on the other the side stories can drag on. Another example of a manga adapted from an LN/WN is Tsuki ga Michibiku Isekai Douchuu / Moon-led Journey Across Another World which has recently thrown two side character stories at us in a row.