This may due to some inexplicable serendipity. It may be due to the fact that the seeker has searched deeply within himself or herself and determined what sort of instruction seems to be required. It may be a combination of the previous factors, or some intuitive awareness beyond expression. For whatever the reason, the saying often applies. Sometimes you can learn what you are seeking from a teacher who is not necessarily a Zen teacher.
Many truths are universal.
Keep your eyes open and watch. Sometimes people are alienated from the religion they were raised in and seek answers elsewhere. If these people were to seek different perspectives in their own faith they might find the answers to their questions. Sometimes by studying Zen for a while one can gain a greater appreciation for one's previous religion and return there with a greater understanding. And sometimes people find just what they are seeking in Zen and make it their personal religion.