Lets try to keep the details of this fight, when, where, all that, toss it in the bin.

Just, what is this?

He was an arcanist originally right? Summoner isn't the rarest of soulstones, he might have been able to encounter one, right?

Instead it looks like he forged his own path completely?

Lithomancy is a form of divination by which the future is told using stones or the reflected light from the stones. The practice is most popular in the British Isles.
Not COMPLETELY from scratch mind you, given the british accent, but...

.. think he might have borrowed an old book from the twins?