It is indeed as you remember the ex-girlfriend that discovered the hostages, so the MC has yet to know about it. However i dont remember if Noelia's father has told them in the letter about what's inside the hole/the mine, because if he did, they should know about that.
Edit : nvm, checked last chapter, the father wrote in the letter about the facility so the MC should know about hostages. Now I can give a bit of leeway if he doesn't connect immediately both informations, but hopefully it won't be a surprise...