Yes, only he has seen them! That Liakopoulos guy claims that he has found the so-called "Copper Books", which were written by Ancient Greeks and include major pre-historical events (like a war between Nephilim and Elohim) and true wisdom. Of course, he doesn't even dare to cite a valid source.
1/4 of his work is taken from Orthodoxy, but he's giving his own interpretations.
1/4 of his work derives from Gnosticism, especially Cerinthus.
1/4 of his work has been influenced by esoteric Judaism (say Kabbalah?).
The rest 1/4 is pure imagination along with some Greek philosophers.