I think the important take-away here is that Rei and Toya both made the same exact suggestion for how Shimada could have moved forward. The lauded genius and master has similar thinking to our MC. There's been a few points in this volume where this has been pointed out. It becomes even more apparent once Rei and Toya have their commemorative match during a much later chapter after Rei wins his first title. They seem to just... click. There's still a massive difference in experience and skill, but there's something there that lets them sense the same things, essentially.
It was a really good set of episodes in the anime.
Like others, I have a hard time following the shogi, but sometimes you don't need to know the significance of a specific move if there's context around it, like in this case. The parallel actions of Rei and Toya here are what you should be noting.
@PiggyIsMe