I read this in 1 of 2 ways to be honest.
1. Personally, it seems a bit out of Character for Yu to not want to talk about Shenmue (especially this very upfront blunt statement), so I'm sure he has been told to only talk about Air Twister. This make sense to promote the game as it's right around the corner, and two, probably is contractually enforced by Apple. Apple are very strict in their approach to most things, so I'd assume that in their contact with Yu they would state specifically that he is NOT allowed to talk about other platforms, and by proxy Shenmue as it's on Steam/PSN etc, which are their direct competitors.
2. There could also be some influence from a potential Shenmue IV publisher in which he has been told to not mention Shenmue. We know how eager Yu has been in regards to hinting about things, most famously the E3 2015 Forklift tweet, which got him in trouble with Sony lol. If a publisher has indeed picked up Shenmue IV, they would most likely want to keep it a secret until it's officially announced for the biggest shock factor. Keeping Yu's lips sealed at this point would be very beneficial and could also be the reason for his statement.
Could be either or.