The rule for being forced to play if you have 13 players eligible was introduced this week if i am not wrong. With the additional clause that each club can ask once for postponement of the match if they have too many cases.
The napoli case now has nothing to do with the protocol. No where in the protocol is stated anything about having doubts of being infected. Officially Napoli has only 2 positive players and therefore must play . If the local authority doesn't allow them to travel its outside of the sport protocol except of that line highlighted above which states smth about inability to play due to measures taken by government authorities.
As i said now its up to lawyers but tbh i wouldn't be surprised that DeLa made this up. In all honestly can't blame Juve for trying to get the 3 points. They don't have the luxury to postpone matches for fun for just 2 players sick on the other team.