They are the SI unit of mass. He's just saying that because it's indicated by lines on the package that the actual measurement is done in volume, and the conversion is implicit by the scaling. Where he goes wrong is in thinking that it's implying that "grams of butter" is a unit of volume.
I live in Europe and have always weighed exactly 100g on the scale, whether I was asked for 100 grams of butter, sugar or flour.