he was a siddha purusha. my interpretation of what it means is you conquer all your base desires and human nature. basically at that point, your origin or religion itself doesn't matter. that enables you to sort of become a vehicle through which paramathma operates.
what is this based on:
he was among the 300 siddha purushas that were initiated by Swami Samartha who is Dattatreya's avatar - this avatar was announced by another of Dattatreya's avatar some 300 years before it happened.
there are accounts of other renowned hindu saint AFTER his time, who had referred to him respectfully as "my old brother".
i think whatever your beliefs, the one that makes you humble and pure matters.