This isn’t the first time Marty has met up with some from 343i. He just had lunch with Frank!! PLEASE THIS 343 FULL SEND IT GIVE US MARTY FOR INFINITE!!!
People talking isn’t proof of anything. Right now Marty has his own games studio building a VR game for Playstation, so it’s unlikely for him to be part of Infinite. There are a couple threads about potential composers for the game, feel free to leave your thoughts there