If he was lying, he wasn't necessarily breaking NDA as NDAs don't generally cover misinforming the public through deception and outright lying.
If he wasn't lying...
1) "When I meant dlc, I meant Fighter Pass! I couldn't check other dlc after that!"
2) "I said I checked dlc, but couldn't find Chief. Also, I didn't say I cracked Fighter Pass to confirm my statement!"
3) He's telling the truth, or at least a half-truth. Maybe Chief might be in and he simply doesn't know about it, as this decision wouldn't be up to him.
Grant Kirkhope didn't know about Banjo in Smash until January of this year. He had assumed it was going to be a Raving Rabbid or something.
Or maybe he was just being coy and speaking i the present tense, like "[At the time of this tweet], Master Chief is not in Smash."
There's also a curious typo in the tweet. "Master Chief
is not is Smash DLC. Although I did just download Smash." Could be nothing, or...