I don't know how NDAs work in football but I'd imagine when Levy sacks a manager they have to sign something that stops them going to the press. If he lets Conte's contract run down then surely he is free to give his story to whoever. I'm sure Levy would rather sack Conte even if its in the last month of the season than risk his and the clubs name being smeared in the media.
NDAs are common practice when managers / DOFs are sacked. And they work both ways.