My understanding is that their teaching was not grounded in right view, which is why The Buddha-to-be did not reach enlightenment following what they taught.
Right view is the first factor of the N8FP, so without it, enlightenment is not possible.
The arupa loka is made up of 4 kinds immaterial realms where one could potentially be reborn in according to their degree of meditation attainment/s. If this is the case, it cannot be imaginative.
