I agree with ishoot10s. If possible take it to another smith. They will be able to tell if the damage was caused by removing the stuck case or not. (Honestly sounds suss to me and I reckon they damaged the barrel trying to remove the case) The only damage to a barrel I can think of, that can be caused on firing, is a bulge or scoring from foreign objects being blasted into the barrel wall by either ignition or the projectile.
I reckon drills and rods were used, which is perfectly fine if you are careful and patient.
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