Pellets that veer out of the main pattern are called flyers. The uncropped photo showed several; one in the upper right hand corner was 4 feet from the pattern's center. How did the pellet wind up so far away? It might have stuck in the wad briefly, either by itself or by "bridging" with other pellets, and when it finally freed itself from the wad, it angled in a different direction. Or perhaps it caromed off another pellet like a billiard ball, maybe even getting dented in the process, making it flare like a Wiffle ball as it encountered air resistance upon exiting the muzzle. However it got where it is, it's out of the main pattern and way off target. Flyers are most common with lead shot, especially with cheap ammo. You'll get fewer flyers if you shoot premium shells containing hard, buffered shot.