I don't know about this specific case to be able to comment directly, but there are times when the supposed cost of damage is calculated to be surprisingly convenient to allow specific charges to be brought. The fact that it is a nice, round figure makes me wonder whether that is the case here.

I haven’t been around the industry for a few years, but I’d wager you could not only repair the frame, but also upgrade the glazing to Tru-Vue Optium Museum Acrylic for that price. So something is certainly suspect.