In Boruto chapter 80, something seemed to be wrong with the protagonist, given how he reacted to the great ordeal he was put into. Kawaki not only sealed away Naruto and Hinata but also got Eida to get their positions switched. This meant that everyone who was after Kawaki was now after the series' protagonist.
The previous chapter saw Kawaki forcing Eida to announce that his brother had killed Naruto and Hinata. Following that, the Hidden Leaf Shinobi went after the protagonist. However, Sarada and Sumire were unaffected by Eida's ability, following which Sarada convinced her father to side with Boruto.
Disclaimer: This article contains spoilers from the Boruto manga.
Why does Boruto not acting resentful seem weird?
In the manga's chapter 80, Kawaki forced Eida to inform Shikamaru that his brother had killed Naruto and Hinata. Kawaki did this after the event when Eida happened to swap Boruto and Kawaki using her Senrigan.
Following Eida informing Shikamaru about Naruto and Hinata's death, the Hidden Leaf Village Shinobi turned against the "outsider." This included Mitsuki, Team 10, Sasuke, and all the other Shinobi except for Sumire and Sarada.
Regardless of what had happened, Boruto stayed calm and confident after witnessing his fate. Considering all the things that happened to him in the short time span, the kind of reaction he gave does not seem normal for a 12-year-old character.
While it is true that he seemed to be at his limits when his Team 10 friends - Shikadai, Inojin, and Chocho - attacked him, he nevertheless seemed alright after his Sasuke grabbed him. While his master backing him should allow him to breathe a sigh of relief, Sasuke himself does not believe that the "outsider" is the Seventh Hokage's son.
The only reason he chose to support the protagonist was because Sarada requested him to while activating the Mangekyo Sharingan. This meant that she had begun to overflow with emotions, typically hinting that there must be some truth behind her words.
Nevertheless, the ordeal the protagonist was put through should have been enough to break him, or at least push him to be a little resentful of Kawaki. However, Boruto remained calm and tried to understand his brother's actions.
While fans believed that this was a sign of the protagonist's mental strength, it could point to weak writing, considering that the protagonist had just lost everything he had, including his family, friends, and his home.
Regardless, fans know that the Seventh Hokage's son is set to be much more calm and serious after the time skip, leading fans to believe that there is a much more cruel path for him in the future. This is why the manga depicted him as being calm and confident, given that his entire personality could switch by the time fans get to see him again.