I read it as both lead down to 7.
From room 6 there is an "official" entrance with a shaft that goes down into 7. The ladder in 3 is behind a trap door and, looking at the floor plan, seems to lead to the bits of rubble in the western corner of 7, four squares west of the shaft from room 6.
Room 6 is easy to find, but has an alarm trap that alerts the trogs. I plan on making the trapdoor in 3 something the PCs need to find; it isn't immediately visible unless they search or the Elf gets lucky. ;) But if they do find it the reward is a sneaky way down behind some piles of mining rubble guaranteed to not rouse the trogs.
I don't know if that's how it was intended when written, but is how I plan to run it :)