注大乘入楞伽經 3.110

3.110

言此不定人聞說三乘法時，隨生信入順學而成，其性可移故言不定。

This means that when these indeterminate persons hear the teachings of the three vehicles expounded, they give rise to faith and entry accordingly and study in conformity to attain completion; because their nature can be shifted, it is called indeterminate.