I believe Leo tapped into Spirit. At some moment his vibrational frequency met with that of a higher thought. Obviously he believed in possibility and used his imagination. He was a reader, so perhaps he read the ancient works by Egyptians.
There was something special about Leo, and lucky for him, he had friends that held key positions in society. He was likable, so when he challenged mid-evil thinking, his friends shrugged it off. After all, they liked the guy. Besides, he was great to have around during social gatherings talking about his inventions and latest conversations with bishops and the Pope. For the superstitious party-pooper, sometime during the evening, Leo would present the antiquated thinker with a quick penciled pocket size portrait of said person, thus creating yet another ally.
His work, some commissioned, shows that he had a deep sense of self and God. He understood Universal Law and the perfection of nature, and since there was nothing to watch on television during the fifteenth and sixteenth centuries, he had plenty of time to transform his visions into physical forms.