^Dry weight isn't just the fuel tank. Between engine oil & coolant, transmission oil, differential oil & brake fluid you can be looking at another 100 lb of fluid, other than fuel.
There are many cars with incorrect weights in the game. Just about every modern Ferrari in GT has a WILDLY optimistic curb weight. I wonder if its some agreement with the factory, its that bad. And if you doubt me be careful looking up Ferrari curb weights online. They usually only release dry weights.