I think you may have tipped the odds favorably with your description of the problem. I hope you have pictures too. The noise and the rapid catastrophic failure after that tells me that the rod bearing lost lubrication rapidly. If some of the other rod bearings show damage, I would say that the oil change people were definitely responsible for the damage.
If the oil change guy claims that all the rods should have flown off at the same time, or similar words, I think you should win because we all know that that is wrong. Judgement for the plaintiff for $3,000.
I have no faith in ASE certification. It doesn’t mean the people are careful. I always thought of it as a joke since I had three years and two months of trade school training.