Did Brother Tom the future-seer know that this illusion would get this kind of response from Byron? Is it just meant to distract him and the others for a few crucial seconds? And even if he did believe it, wouldn’t they just attack after they finished surrounding him anyway?

Mmm, probably yes to all three, but I do wonder how Tom might’ve handled things if Byron had turned out to be “that stupid,” or more charitably, desperate to believe in a miracle and that his own memories were lies. Doing that quasi-Irish accent convincingly and pulling out details like “he can’t grow a full beard” most likely means they’re casting a spell keyed to memory. (Although I find it hilarious to imagine that Homon, using HR’s knowledge of Byron’s backstory, has done a ton of coaching Tom to play this bit part. “All right, I think ‘ye’ have the speech pattern down. Now just keep tryin’ to turn everythin’ into a ‘lesson’ and hazin’ everyone affectionately and you’ll be fine.”)

I guess the best-case scenario, from their perspective, is that they could’ve led Byron back to Cultist camp without a fight, but it’s hard to imagine even a self-deceptive Byron abandoning his post for his past. And all that would be needed to shatter this illusion would be for someone to point out that Bayen and Brayen still have their axes in their hands, the same ones that Byron now carries in their honor.