PC of Underrail is a natural psion. Now depending on what exactly that means within the general/expanded lore it might be significant... or not. Even if you play the game as a non-psion, i.e., character who didn't choose to use psionics, you're still a natural psion.
Since Hadrian Tanner has been doing his thing for a while - Old Jonas of SGS said that Tanner joined when he was still young, I'd assume that Tanner has developed an eye for gifted humans and thus chosen PC of Underrail for that very specific reason. After all Tanner, for whom the Faceless Cube is extremely important, tasks PC of Underral above everybody else to go and retrieve it.
Somebody who did a review of Underrail recently suggested that Psionism is somehow related to the Godmen - admittedly a race of beings superiour in every way to humans, as Six has shown. If Psionism is indeed originating from them, be it a technology, or a natural talent, it manifesting in humans should mean that they are somehow exceptional. The Lunatics seem to be playing a certain role with that, as even though they are abundant, they're also insane, which could mean that using those devices to teach yourself Psionics can be detrimental to most, as the Psychokinesis teacher at SGS himself suggests. The fact that PC of Underrail can use those without any negative effects(at least so far) could further solidify the fact that they are somehow exceptional compared to normal human beings.