One small cheat?

We all agree this one, as far as twists go is pretty air tight.

And I think it's pretty much universally agreed that by the end we understand that Cole knew Malcolm's true nature all along.

But when Cole is having his confession with Malcolm in the hospital, I believe there is one instance of dialog that was inserted in to toss us off the scent. Cole makes Malcolm promise to never tell anyone his secret. We read this the first time as "Don't tell my mom." But if Cole knew all along, he wouldn't feel compelled to make Malcolm keep his secret. I think this is the one thing on re-watch that I feel Is a small cheat.