I came up with this theory recently I dont believe myself (I know strange) but here it is.
So when the doctor woke up from the dream crabs he found old Clara but that wasn't real so what about the others? Were they still dreaming as well? And also the doctor wakes up on the volcano where Clara thinks she chucks the Tardis keys into the lava so maybe those patches have a bit of dream crab in them?
I know it is stupid but it gets you thinking.