Ore selection in Demon Slayer anime
It is mentioned in the &quot;Kimetsu No Yaiba Manga : Chapter 6&quot; that :
He utilizes the Water Breathing: Fourth Form - Striking Tide to slice the 'threads' that he smelled, and successfully defeats the demons .
Though it's not mentioned anywhere, what I assume is by the time he completed final selection , he had defeated many demons as well as cut the rock with the help of his smell and breathing technique. So , even when he was asked to choose the ore , he chose to use the sense of smell as he didn't have any other parameter or knowledge to do so .  So he chose smelling similar to his past actions.