from a certain point of view everyone is a Buddhist, from another, no one is...
To paraphrase the Diamond Sutra, Chapter 3...
"Eventually all living beings will be led to Nirvana, and yet, even after all have been liberated, from the perspective of a bodhisattva not even a single being will have actually been liberated."
"Why? Because a bodhisattva does not cling to the arbitrary illusions of form, name or phenomena such as an ego, a personality, a self, a separate person, a separate religious tradition, or a universal self existing eternally..."
This is the basis for the saying that one’s Buddha nature is realized at the moment when the desiring self is no longer a self desiring, even a self desiring to become a buddha.
And that is one of the most fundamental pillars of Buddhism.
May the force be with you