The author doesn’t claim that the engineer is **not at all** responsible for the train wreck. She claims that Acme Engines should be held liable, but this doesn't imply that the engineer doesn't also bear some responsibility.

The author doesn't suggest we know what would have happened if Acme Engines had remodeled their older locomotives. The fact they spent $500,000 remodeling the newer ones is just evidence that Acme knew the knee-height switches were a safety hazard.

The author tells us that the wreck happened when a knee-height switch was accidentally struck. The fact that Acme Engines spent $500,000 remodeling newer locomotives doesn’t explain the cause of the wreck.

If anything, Acme Engines spending $500,000 to remodel new locomotives suggests that knee-height switches might be hazardous. The author doesn't suggest that knee-height switches are **not** hazardous.

The author states Acme Engines is unlikely to spend $500,000 on a mere inconvenience. This implies that the $500,000 was spent for a different reason—safety concerns. The author uses the fact Acme Engines spent $500,000 relocating its knee-height switches to suggest Acme Engines knew those switches could be a safety hazard.