When he says "short a card saying otherwise," he's talking about
Brothers Yamazaki XD
Also keep in mind that the legendary rule is different, slightly, for Planeswalkers. For a legend card, you can have multiple legendary
creatures, as long as they don't have the same exact name name (for example, you can have Dragonlord Dramoka and Dramoka, The Eternal out at the same time). However, you can't control a Planeswalker at the same time as another planeswalker of the same character subtype (so you can't have
Jace, Memory Adept and
Jace, Architect of Thought at the same time, because they're the same Planeswalker - Jace).