Deductive reasoning is the art of drawing a conclusion through deduction. From a hundred possibilities, those that don't meet or make the criteria to logically explain cause and effect are being deducted until only one possibility is left.
But because Emeros had used his Gauge ability upon contact with Rizal, he managed to do the opposite.
He saw the particular magical crystals and energy stones that he had used. Since Elemental Cores were rare, other rocks, ores, and magic crystals were used. But unlike the Core, it could not gather and grow energy independently and needed to be recharged.
From the specific truths of Rizal having the stone, Emeros added and added possible facts about it. Inductive reasoning was used to 'explain' Rizal's general symptoms.
But of course, the specific symptoms could not manifest to everyone, even on Rizal. But with the power Pseudos, these half-baked details seemed more convincing.