"But it's not the truth, is it? Your disciples didn't kill you for any righteous reason, they killed you for selfish reasons." Rio replied, his words changing the world around him once more, where the vision and character started shifting according to the story he told.
"The gods promised them power, and the mortal realm to rule _ and they agreed instantly."
"Cause if their actions were even slightly righteous, their faces wouldn't show the smiles of relief, or the grin of victory when they killed you, but the glossing of guilt and tinge of regret."
From the novel, Rio knew Aelthar was a god stuck in past, at the time of his death - he didn't need anything else other than a mirror to show him the truth.
An answer which could clear his lingering doubts, regrets, and obsession. — and since Rio was no therapist himself, he just copy-pasted what Leon said to get Aelthar to move on.