As usual, Neal has it right ... It looks like a sloppy drywall guy did not mud the tape joint enough originally. With temp and humidity changes, you got a crack (not structural) in the finish of the wall.
1. Using a fresh razor knife (utility knife or box cutter), trim the paper tape off and clean up the surface with sand paper
2. Buy a small tub of pre-mixed drywall compound. Spread it smoothly over the repair area, feathering slightly beyond the area itself. Use a 6" plastic spatula for drywall.
3. Let dry completely. Touch sand smooth and to feather the final surface.
4. Prim and pain.
5. Have a beer and congratulate yourself for saving big money!