Passive mobs such as cows, sheeps, pigs, and even tamed mobs such as wolves, cats, and parrots can follow spectator players, despite they can't physically and visually see them.

How to Reproduce
1. Spawn some passive mobs.
2. Use their food (wheat for cows/sheeps, carrots/potatoes for pigs) to follow you.
3. Switch to spectator.
4. Move around.

Observed Result
Passive mobs can follow you despite you being in spectator mode.

Expected Result
Passive mobs should ignore spectator players.