Not abiding anywhere means that one does not abide in good and evil, existence and nothingness, inside, outside, or in between.
Not abiding in emptiness and not abiding in non-emptiness, not abiding in concentration and not abiding in the absence of concentration, that is not abiding anywhere.
Only this not abiding anywhere is the true abode. When one attains this, it is called the non-abiding mind. The non-abiding mind is the Buddha mind.