The damage you see on that chair, if it is indeed a gunshot, is from a single projectile.
A shotgun slug would be a single projectile, but much larger than the damage shown. And with enough impact to rip that seat apart - a whole lot worse than what’s shown.
A shotgun with 00 buckshot would have 8 projectiles, tightly grouped. I would expect to see either multiple points of impact, or perhaps what would appear to be one really big point of impact.
A shotgun with birdshot would have a lot of very small projectiles. No idea how many, I’ve never counted them. It would leave a big area of damage but not a lot of penetration.
I’m thinking a handgun, maybe somewhere between a 9mm and .40 cal. A single bullet, maybe as round as your little finger, that would pass through that chair from front to back at an upward angle.
And due to that angle, I don’t think the chair was sitting on the floor like a chair is supposed to be sitting when it was hit.