They mentioned other kodokus at the start (with the dead toddler), I think he's just a victim of another one and isn't Reiji.
Edit: I misremembered, they didn't say there were more. The random dead toddler at the beginning makes me think something else like that is up, I don't think Reiji-vee would forget that he just ate a kid. Could be wrong though since both of them clearly block out memories.