Why do pidgeys and rattatas still appear even if not in sightings?
There are more possibilties:
- Your data in the tracker is not synchronized yet, but the information for the pidgey is already downloaded.
- It just spawned there.
- The list is already full with other Pokémon (can happen, probably not with pidgey or rattata but though).
When you reopen the App with a good Internet connection the tracker should be loaded accurately.