What do you think this means? I've been seeing harpsichords being transported in cars for years? Are there regulations that forbid doing so? Sooner or later, I hope that I too can learn to play the harpsichord and CARRY IT WITH ME.
Perhaps the yellow flames (police) were not familiar with the harpsichord and thought that the device, apparently similar to a piano, should be considered an "exceptional" load.
In reality, at least the one pictured in the photo will weigh only a few dozen kilos, and even more so if transported in its case inside a van, it becomes any normal, albeit delicate, piece of luggage.
Even the vehicle's immobilization... I take note of the lawyer's opinion, but I would have appealed the sanction anyway, if only as a matter of principle (especially since the lady already has a lawyer in the family).
Besides, every law must be interpreted and applied with common sense.