At any given moment, even when he was alone, there were a number of beings keeping an eye on Lex. Since his system had a soul, it could somewhat be considered a being, and since it was inside Lex's soul, it was more or less paying attention. Mary, too, had a permanent connection to Lex, and so could connect to him whenever she wanted.
There was that mysterious being from the Primary realm who just decided to pop into the Inn one day. It was unlikely he ever consciously paid attention to Lex, but a being of his caliber would always be aware of anyone he had ever paid attention to.
Moreover, not only could he see Lex, he could foresee exactly how his entire life would play out from a single glance. It was not prophecy that he would use, just probability and prediction. The scale upon which such a being operated was outside the realm of understanding of mere mortals life Lex.
