this cheeky fucker knew exactly what was gonna go down a month in advance

I have a hard time believing that Byleth's reveal and development was truly a "well hidden" fact around the team as he said… Like, this reeks of Nintendo's decision no matter how you see it, and the character is already pretty much fully developed. How would you keep THAT any more a secret than Terry, who barely had anything to show for him on the reveal itself..?