Nowhere is he saying anything about the F1-75.
He was appointed as Haas's TD on December 4th, 2020. So the last time he may have had any input into the F1-75 was November 2020, that's 15 months before the cars hit the track for the first time, far too early to know anything other than some very high-level details about the car. Not to mention no way Ferrari would've willingly let him go to Haas had he had a major role in the F1-75.
Besides, Turrini usually writes in a way that's practically indecipherable.