Well, he stumbled upon "it".
But he doesn't know what he'd found, much less how to go about reaching it again.
I do like the contrast with the Yamamoto classmate - not technically proficient by Yoshida's estimation, but that humanistic connection to the grandmother, makes the expression come forth. There's something there that resonates with the other students, intrinsic to the human experience, that goes beyond mechanical precision and mastery.
I wager Yoshida's main struggle will be figuring out that connection, that "expressive"ness as the teacher put it, as far as this title goes. And Tessera will likely be his bridge to that point, and he himself will be primary obstacle, though obfuscated as he pushes the onus onto others like this Senba character, or his teachers and parent and classmates.
But, this remains an intriguing series, and I look forward to more.
Thanks for the TL work as always.