That's because a 'picture' displays in the viewport, not the map.
It's not really following your character (you can see this if you go near the edge of the map, where the character is not centered.),
it's remaining at the same location on the screen.
For lighting effects, I usually use a fog, which gets located on the map, rather than the viewport.
Another option would be to make a character set with your 'glow' effect as one of the poses, and use an event on the campfire with that graphic (no animation, Direction Fix ON).
Be Well