Necroduality is reinforcing the opponent’s zombies when they come into play. Wording on the card specifies, “when a non-token zombie creature enters the battlefield under your control: Reinforce that creature X times, X is this support’s shield.” This is directed at tye owner of the support, not both players.
If this was for all players it would be worded “when a non-token zombie creature enters the battlefield under any player’s control: Reinforce that creature X times, X is this support’s shield.”
I believe this is a bug.