Bulge in drywall after mounting tv
You do not need to be concerned, assuming that your lag screw is anchored into the framing. 

That's a result of a pre-existing gap behind the drywall. Maybe some insulation or a wrinkle in the vapor barrier held it out during initial hanging, and your lag screw pulled it in tight. Because there was a drywall screw there holding it out the surface bulged as the rest pulled in. There are no apparent structural concerns. 

If you ever remove the tv, you'll want to put a pair of drywall screws above and below the bulge before removing the lag screw. Then remove the tv mount, cut away the bulged drywall and repair.