How many kilograms of graphite are consumed while producing 4 kg of Al through Hall-Heroult process?
According to Aluminium Production1:

The production of 1 ton of aluminum typically requires 420 kg of carbon, 1920 kg $\ce{Al2O3}$, and 16 kg $\ce{AlF3}$ ....
The theoretical carbon consumption is only $\pu{333 kg C/t} \space \ce{Al}$. The excess carbon consumption is mainly due to air oxidation of the hot anodes in the hooded cells. The reaction occurs preferentially in the pitch binder matrix and leads to the physical loss of coke particles to generate dust that floats on top of the electrolyte.

Theoretically, your answer holds good. However, it fails practically. It's a stupid tricky question by the problem setters, who are apparently testing your knowledge of metallurgy rather than stoichiometry.
References:

Tabereaux, Alton T., and Ray D. Peterson. “Aluminum Production.” Treatise on Process Metallurgy, Elsevier, 2014, pp. 839–917. doi:10.1016/B978-0-08-096988-6.00023-7