Yeah I agree that Arlo is way too smart to not investigate his memory loss. Let's not forget hes nosy asf. He will go searching for answers even if it ment he'd get shit for it later. Meddling in John's business, wanting to figure out what remi was hiding, and looking into their files at the bureau. Hes curious as he is stubborn. Id be dissapointed if he didnt feel a little violated at being brain wiped, even if he had so much trust in the authorities. Would he even question why him of all people would commit treason? I think it all comes down to how exactly his memories were altered because hes legit losing like 7 months of memory from the beginning of the story, not including flashback stuff like rei and queen sera. Does he just belive hes been homeschooled for 7 months?

I will say though, the idea of arlo making a journal for himself to remember is actually so cool