I'm assuming that was one of the lowest ranked dungeons in this world, and it was considered rank C. Usually the ranking systems go lower than that, but I guess C is the lowest here.
Also, what was with that unnatural panty close up? That was a weird fan service to randomly throw in.
On another note, it feels a bit rude not reassuring her after worrying her by showing his new status considering he's shown it before. Certainly, not sharing your status is probably the norm and he does have a "secret" grinding method that is worth hiding, but he doesn't seem that concerned about it. Especially with her.