It is irrelevant because that GM is using a different gun.
It is generally standard practice to not pay for return shipping unless the product is incorrect or defective. I'm not sure which of those terms applies to what you received, but it is definitely one or the other.
I’d go with incorrect product. Box says .358. Bullets are .357 and they admitted to using a .357 sizer. I assume (again, I don’t reload) that a .357 sizer produces .357 caliber projectiles and not the advertised and sold as .358?
Edit- are there accepted tolerances with advertised projectile calibers?