I was wondering the same thing. I thought it was a misprint. In case anyone is wondering the same thing this is the calculation:
Gallons per BBL 31.5
BBL Dosage 10g per 10 BBL or 1 g per BBL
31.5 x 10 = 315 gallons / 5 gallons = 63 doses
10 g / 63 doses = 0.158 g per dose for a 5 gallon batch
Most home scale only goes to tenth of a gram so 0.1 and a pinch should do it.