So to summarise:
1) ASL recommended a voluntary isolation after the Genoa game, which Napoli did not follow.
2) Napoli cancel their tickets to Turin on Saturday and decide not to show up. They do not release an official statement indicating their decision not to travel.
3) On Sunday, the ASL tell Napoli not to travel. Milik travels for international duty any way.
So, Napoli did not obey the first ASL recommendation, and would not have been affected by the second one if they had travelled on Saturday. They did not obey the second decision either, because Milik travelled to play for Poland.
During all this time, Napoli did not release a single statement to clarify their position, probably because Juve, Serie A and even the Campania ASL would have called them out on the spot.
This is a simple case of Napoli acting in bad faith and taking advantage of the chaotic situation in Europe and the rest of the world.
They do not have a leg to stand on, as far as the appeal is concerned.