Rear axle can easily be bent from being nose-high, because it shifts the weight to the rear axle. If the axles are already borderline on their capacity, which appears to be the case from looking at the original pictures, it would not take much to overload and bend the rear axle.
Running nose-high is partially your fault, but the dealer should have tried to upsell you on a lift modification for the trailer so it would tow level. If he had done that to begin with, you could have avoided this problem entirely.