首楞嚴義疏注經 1.258

1.258

定其相外。外，猶離也。心既離身，不相干涉，如前所答一人食時不令眾飽。

This determines that they are external to each other. "External" is like being separated. Since the mind is separated from the body, they do not concern each other, just as in the earlier reply that when one person eats, it does not cause the multitude to be sated.