Pre-existing rod bearing damage or NEW damage caused by forgetting to add OIL during OIL change?

I test drove a vehicle, did a visual and audio inspection and then bought the vehicle. Drove it on the Highway with no problems. 2 days later drove it on the highway with no problems and had the oil changed. Drove it half a mile to get an alignment, after which, I started it and I heard a slight knocking. I brought back to the people who changed the oil, and they changed the oil again but the knocking continued. I Asked the mechanic what he thought it was and he responded that it sounded like a bottom knock. He then explained it by telling me it sounded like a rod bearing had spun. I asked him if it was OK to drive because I didn't live close? He said YES but I would have to take it easy. I went 5 miles or so and the knocking increased 10 fold and the engine performance degraded badly so I STOPPED on the side of the road and shut it down. I had a auto shop inspect and they found very worn bearings for cylinder 1 and 2 (see pics) and damage to the journal on the #2 cylinder (no pic). The mechanic said this was a result of the engine being run with NO OIL.

A insurance inspector disagreed with my mechanic and said the damage was pre existing by the journal damage he saw, because of the metal flaking in the oil pan(see pic) and no colorization to the damaged journal. The inspector also noted the oil screen was clean.

My mechanic said there would have been some kind of signs of that kind of damage before hand and it would have been heard. He also stated that the metal flaking in the oil pan would have been caused from a sudden wear down of the bearings and journal. He stated that colorization or burning of the journal is something that would have happened over time and that their was no colorization because the damaged happened abruptly.
NOTE: I've also asked other mechanics at auto shops and they lean towards my mechanics view.

I'll have the block replaced within a week, at which time my mechanic will break down the old block further so we may see the whole crank shaft/ other journals and the other 2 rod bearings. Once this is available to be viewed I will call the insurance company again and have them send an inspector once again. They told me they can't guarantee it won't be the same guy! Great!

-PLEASE HELP! The insurance adjustor for the company who changed my oil (a well known BIG Company) has an opinion that is outweighed so far by other Certified Mechanics. This new block is costing me $4100 (Labor and parts).

Respectfully,
Paul