Those are very high doses of each. An average multivitamin has 1.8 mg of B6 (vs. 20 mg in the study) and 6 mcg of B12 (vs. 55 mcg in the study).
I am surprised anyone wants to take that much, but I guess the smokers were trying anything they could (short of actually quitting) to compensate for the effect their habit has on their health.
I was referring to multivitamin levels which are typically ~100% RDA, so to get the levels the study considered harmful, you have to be intentionally taking large doses of B Vitamins which is easy not to do.
I am surprised anyone wants to take that much, but I guess the smokers were trying anything they could (short of actually quitting) to compensate for the effect their habit has on their health.