Yeah that's because they used .box as a custom TLD for decades and either didn't get the introduction of .box as a legitimate TLD or failed to secure fritz.box in time.
Not the first time this has happened, and likely won't be the last either.
Currently the fritz.box domain seems to be owned by AVM (the makers of the FritzBox). Maybe it was just not existing and the local resolver on the box got confused? The domain was created in January and updated only a few days ago so things might actually have changed in the meantime...
