In the overworld, NPCs will not count the Pokémon following you as a soild object, and will walk through it when possible.
There is also a slim chance that you and the NPC walk to the same place at the same time and walk through eachother, but I lack the proof for this.
(My Celebi is occupying the same space as this NPC.)
There is also a slim chance that you and the NPC walk to the same place at the same time and walk through eachother, but I lack the proof for this.
(My Celebi is occupying the same space as this NPC.)
