Boruto fans have been trying to analyze the behavior of Kashin Koji for a while, especially after the revelation of his Ten Directions ability, which grants him the power to see multiple different futures. Therefore, there is a growing theory that his words have a pattern when he is lying and when he is telling the truth, which can be connected with how Ikemoto displays his eyes in the manga.
It has been theorized by a section of the Boruto fandom that Kashin Koji is hiding information from the protagonist, and this can be shown through the way one of his eyes is covered when he is not telling the whole truth. Moreover, this would be a subtle way to tell the reader that there is more than meets the eye, and perhaps he has seen a future with Ten Directions that needs to be kept a secret.
Disclaimer: This article is a speculative theory and reflects the writer's opinion.
Explaining how Ikemoto's usage of Kashin Koji's eyes says a lot about Boruto

Fans have theorized for a long time that Kashin Koji has been hiding information from the protagonist because of his Ten Directions ability, which perhaps allowed him to see a future that requires certain actions to be made. In that regard, there could be some instances where Ikemoto has portrayed the character as lying or hiding information through the way his eyes are covered on the page.
For example, during a flashback scene in chapter 13 of Two Blue Vortex, the protagonist mentions that he is not going to accept a future where Kawaki dies, with Kashin Koji hiding one of his eyes in silence. This, in a way, could be interpreted as the man knowing that Kawaki is bound to die at some point in this conflict and simply doesn't want to say anything about it.
Then, when focusing on chapter 21, he is seen having a similar look when he is asked whether Konohamaru survived against the Shinju clone Matsuri, which maintains this pattern. While it can be viewed as forced analysis when applying this to just one character, there are several examples, such as Amado, where Ikemoto has used a similar strategy.
Why would Kashin Koshi be doing this

Many fans have come up with the rationalization that Kashin Koji is hiding information from Boruto because he wants certain events to play out so they can get the best possible future from the ones he saw with Ten Directions. It would make sense given the fact that he doesn't want to do anything that could lead to a different outcome, which is why he needs to lie or keep things a secret.
Furthermore, the aforementioned case with Kawaki is quite telling since it could suggest that a confrontation with that character and his upcoming death seems inevitable, although the original series already dealt with a similar conflict regarding Naruto and Sasuke. Therefore, this is something that would make sense for the character to do, especially considering his mentality and motivation to help the protagonist.
Final thoughts
Kashin Koji has valid reasons to hide information from the protagonist, and this is something that could reinforce the theory of his eyes working as a way to tell the reader that he is lying. It also adds another layer to Ikemoto's visual storytelling in the manga.
Related articles:
- Boruto: Two Blue Vortex chapter 21 sees Sasuke's return (but not in the way fans expect)
- Boruto: Two Blue Vortex confirms Yodo's fate with chapter 21
- Kashin Koji may not know about Boruto's Jougan (& the Dojutsu's potential role shows why)
- Boruto: Two Blue Vortex chapter 21— Sarada unveils her Mangekyo Sharingan ability as Boruto defies Koji