In Coco, Miguel's stray dog Dante goes with him into the spirit world. I thought at first that he become a spirit too because he stole food from offerings in the graveyard, thus stealing from the dead, thus becoming cursed.
However, later in the movie he becomes a full-fledged Spirit Guide, and in the end of the movie, he and Innelda's guide, a stray cat, are shown alive and well in the living world.
How and why did Dante become a Spirit Guide, while still being in the living world?