Not a novel reader, but I read a lot of comments and I also want to share my opinion.
While this chapter might lack direct explaination, we already got everything from previous chapters.
We know from the rabbit man that the old man in the mine that took care of mc and his 'sister' was not just an old man. So, if before Reiji had 1 question and 1 goal, he now has at least 2 question and 2 goals: for finding his sister and asking why she's acting like that, he now wants to know what the old man wanted to do too.
So he'll need to travel the world....and this ain't mushoku tensei, eva isn't eris, she won't learn swordmanship and be a beast of a fighter....the trip will be dangerous and reiji wants to play it safe.
Besides, there are no sign reiji has those kind of feelings for his sister....but we now know he loves eva. So that's that.
And to end....I mean, the knight following them....most likely a plan to give the two a bit of time to talk and say goodbye