It’s really none of our business to gossip whether someone is enlightened or not. But for the sake of asking a question and then answering it, here are some thoughts:
The best and surest way to know whether a certain person is enlightened or not, is to become enlightened yourself. For how would you know if someone is enlightened if you do not know what enlightenment is all about?
A spiritual guru may be viewed as enlightened by thousands and even millions of followers, and this is why they follow him in the first place. The followers believe, or they have faith, that he is an enlightened being, and thus he has the power to help bring about their own enlightenment or salvation.
Either that they believe they have something to get from following a guru (or a certain religion), or they just follow the crowd for the sake of being seen as religious or spiritual.
It can also be the case that a spiritual guru has so much charisma and radiance by virtue of being enlightened indeed, and these qualities alone are enough to attract followers who are drawn to the guru’s magnetism.
Being a spiritual guru, complete with followers does not, of course, attest to a person’s enlightened status. An enlightened person may be somewhere in the wilderness or desert with no followers or students, but have only the plants, the animals, the night sky, to keep him good company.